Method for reporting channel state information in wireless communication system, and device therefor

ABSTRACT

Disclosed herein is a method for reporting channel state information (CSI) of a terminal in a wireless communication system. The method includes: measuring a CSI-RS (reference signal) transmitted from a base station through multiple panels; and reporting CSI generated based on the CSI-RS measurement to the base station, wherein, when the terminal reports a WB (Wideband) panel corrector and SB (Subband) panel corrector for the multiple panels as the CSI, the WB panel corrector and the SB panel corrector are reported with different bit widths.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method for reporting channel state informationand a device that performs/supports this method.

Background Art

Mobile communication systems have been developed to provide voiceservices, while guaranteeing user activity. Service coverage of mobilecommunication systems, however, has extended even to data services, aswell as voice services, and currently, an explosive increase in traffichas resulted in shortage of resource and user demand for a high speedservices, requiring advanced mobile communication systems.

The requirements of the next-generation mobile communication system mayinclude supporting huge data traffic, a remarkable increase in thetransfer rate of each user, the accommodation of a significantlyincreased number of connection devices, very low end-to-end latency, andhigh energy efficiency. To this end, various techniques, such as smallcell enhancement, dual connectivity, massive Multiple Input MultipleOutput (MIMO), in-band full duplex, non-orthogonal multiple access(NOMA), supporting super-wide band, and device networking, have beenresearched.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method fortransmitting/receiving channel state information (CSI).

Furthermore, an object of the present invention provides a method fortransmitting/receiving control configuration information which istransmitted to support the transmission/reception of channel stateinformation of a terminal.

Furthermore, an object of the present invention provides variouscodebooks for CSI report/feedback. In particular, an object of thepresent invention provides a new codebook for supporting beamformingthrough multiple panels newly introduced in NR.

Technical problems to be solved by the present invention are not limitedto the above-mentioned technical problems, and other technical problemsnot mentioned herein may be clearly understood by those skilled in theart from description below.

Technical Solution

In an aspect of the present invention, there is provided a method forreporting channel state information (CSI) of a terminal in a wirelesscommunication system. The method includes: measuring a CSI-RS (referencesignal) transmitted from a base station through multiple panels; andreporting CSI generated based on the CSI-RS measurement to the basestation, wherein, when the terminal reports a WB (Wideband) panelcorrector and SB (Subband) panel corrector for the multiple panels asthe CSI, the WB panel corrector and the SB panel corrector are reportedwith different bit widths.

Furthermore, the WB panel corrector and the SB panel corrector are usedfor phase correction between the multiple panels.

Furthermore, a bit width of the SB panel corrector is shorter than a bitwidth of the WB panel corrector.

Furthermore, the bit width of the SB panel corrector is 1 bit, and thebit width of the WB panel corrector is 2 bits.

Furthermore, the WB panel corrector is reported based on QPSK(quadrature phase-shift keying), and the SB panel corrector is reportedbased on BPSK (binary phase-shift keying).

Furthermore, when the reporting only the WB panel compensator as theCSI, the WB panel corrector is reported with a bit width of 2 bits.

Furthermore, the number of panels is set by higher-layer signaling.

Furthermore, the reporting of the WB panel corrector and/or the SB panelcorrector is set by the higher-layer signalling.

Furthermore, the WB panel corrector and the SB panel corrector arereported in a PMI(Precoding Matrix Index) in the CSI.

Furthermore, the WB panel corrector and the SB panel corrector arereported independently for each of the multiple panels.

In another aspect of the present invention, there is provided a terminalthat receives a channel state information-reference signal (CSI-RS) in awireless communication system, the terminal including: a radio frequency(RF) unit for transmitting and receiving a radio signal; and a processorfor controlling the RF unit, wherein the processor measures a CSI-RS(reference signal) transmitted from a base station through multiplepanels, and reports CSI generated based on the CSI-RS measurement to thebase station, wherein, when the terminal reports a WB (Wideband) panelcorrector and SB (Subband) panel corrector for the multiple panels asthe CSI, the WB panel corrector and the SB panel corrector are reportedwith different bit widths.

Furthermore, the WB panel corrector and the SB panel corrector are usedfor phase correction between the multiple panels.

Furthermore, a bit width of the SB panel corrector is shorter than a bitwidth of the WB panel corrector.

Furthermore, the bit width of the SB panel corrector is 1 bit, and thebit width of the WB panel corrector is 2 bits.

Furthermore, the WB panel corrector is reported based on QPSK(quadrature phase-shift keying), and the SB panel corrector is reportedbased on BPSK (binary phase-shift keying).

Advantageous Effects

According to an exemplary embodiment of the present invention, aterminal may smoothly derive CSI and give feedback about it to a basestation.

Furthermore, according to an exemplary embodiment of the presentinvention, a codebook for NR to which a multi-panel array is newlyadapted is defined, thereby solving the ambiguity of which codebook isto be applied to NR.

Furthermore, according to an exemplary embodiment of the presentinvention, different bit widths are defined for a WB panel corrector andan SB panel corrector by taking SB characteristics into consideration.Thus, accurate CSI may be reported to the base station withoutsignificantly increasing signaling overhead.

Advantages of the following embodiments are not limited to theaforementioned advantages, and various other advantages may be evidentlyunderstood by those skilled in the art to which the embodiments pertainfrom the following description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included herein as a part of thedescription for help understanding the present invention, provideembodiments of the present invention, and describe the technicalfeatures of the present invention with the description below.

FIG. 1 illustrates the structure of a radio frame in a wirelesscommunication system to which the present invention may be applied.

FIG. 2 is a diagram illustrating a resource grid for a downlink slot ina wireless communication system to which the present invention may beapplied.

FIG. 3 illustrates a structure of downlink subframe in a wirelesscommunication system to which the present invention may be applied.

FIG. 4 illustrates a structure of uplink subframe in a wirelesscommunication system to which the present invention may be applied.

FIG. 5 shows the configuration of a known MIMO communication system.

FIG. 6 is a diagram showing a channel from a plurality of transmissionantennas to a single reception antenna.

FIG. 7 illustrates reference signal patterns mapped to downlink resourceblock pairs in a wireless communication system to which the presentinvention may be applied.

FIG. 8 is a diagram illustrating resources to which reference signalsare mapped in a wireless communication system to which the presentinvention may be applied.

FIG. 9 illustrates resources to which reference signals are mapped in awireless communication system to which the present invention isapplicable.

FIG. 10 illustrates a two-dimensional (2D) active antenna system having64 antenna elements in a wireless communication system to which thepresent invention is applicable.

FIG. 11 illustrates a system in which a base station or a UE has aplurality of transmission/reception antennas capable of forming AASbased three-dimensional (3D) beams in a wireless communication system towhich the present invention is applicable.

FIG. 12 illustrates a 2D antenna system having cross polarization in awireless communication system to which the present invention isapplicable.

FIG. 13 illustrates transceiver unit models in a wireless communicationsystem to which the present invention is applicable.

FIG. 14 illustrates a self-contained subframe structure to which thepresent invention is applicable.

FIG. 15 is a schematic diagram of a hybrid beamforming structure fromthe perspective of TXRUs and physical antennas.

FIG. 16 is a schematic diagram of a beam sweeping operation forsynchronization signals and system information in a DL transmissionprocess.

FIG. 17 illustrates a panel antenna array to which the present inventionis applicable.

FIG. 18 illustrates candidate beam group patterns for L=2 in a 2D portlayout applicable to the present invention.

FIG. 19 illustrates candidate beam group patterns for L=4 in a 2D portlayout applicable to the present invention.

FIG. 20 is a view illustrating a non-uniform port array according to anexemplary embodiment of the present invention.

FIG. 21 is a view illustrating GoB for N1=4, O1=4, N2=2, and O2=4according to an exemplary embodiment of the present invention.

FIG. 22 is a view illustrating a window configuration method for N1=4,O1=4, N2=2, and O2=4 according to an exemplary embodiment of the presentinvention.

FIG. 23 is a flowchart illustrating a method for a UE to report CSIaccording to an exemplary embodiment of the present invention.

FIG. 24 illustrates a block diagram of a wireless communication systemaccording to an exemplary embodiment of the present invention.

MODE FOR INVENTION

Some embodiments of the present invention are described in detail withreference to the accompanying drawings. A detailed description to bedisclosed along with the accompanying drawings are intended to describesome embodiments of the present invention and are not intended todescribe a sole embodiment of the present invention. The followingdetailed description includes more details in order to provide fullunderstanding of the present invention. However, those skilled in theart will understand that the present invention may be implementedwithout such more details.

In some cases, in order to avoid that the concept of the presentinvention becomes vague, known structures and devices are omitted or maybe shown in a block diagram form based on the core functions of eachstructure and device.

In this specification, a base station has the meaning of a terminal nodeof a network over which the base station directly communicates with adevice. In this document, a specific operation that is described to beperformed by a base station may be performed by an upper node of thebase station according to circumstances. That is, it is evident that ina network including a plurality of network nodes including a basestation, various operations performed for communication with a devicemay be performed by the base station or other network nodes other thanthe base station. The base station (BS) may be substituted with anotherterm, such as a fixed station, a Node B, an eNB (evolved-NodeB), a BaseTransceiver System (BTS), or an access point (AP). Furthermore, thedevice may be fixed or may have mobility and may be substituted withanother term, such as User Equipment (UE), a Mobile Station (MS), a UserTerminal (UT), a Mobile Subscriber Station (MSS), a Subscriber Station(SS), an Advanced Mobile Station (AMS), a Wireless Terminal (WT), aMachine-Type Communication (MTC) device, a Machine-to-Machine (M2M)device, or a Device-to-Device (D2D) device.

Hereinafter, downlink (DL) means communication from an eNB to UE, anduplink (UL) means communication from UE to an eNB. In DL, a transmittermay be part of an eNB, and a receiver may be part of UE. In UL, atransmitter may be part of UE, and a receiver may be part of an eNB.

Specific terms used in the following description have been provided tohelp understanding of the present invention, and the use of suchspecific terms may be changed in various forms without departing fromthe technical sprit of the present invention.

The following technologies may be used in a variety of wirelesscommunication systems, such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), and Non-OrthogonalMultiple Access (NOMA). CDMA may be implemented using a radiotechnology, such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented using a radio technology, such asGlobal System for Mobile communications (GSM)/General Packet RadioService (GPRS)/Enhanced Data rates for GSM Evolution (EDGE). OFDMA maybe implemented using a radio technology, such as Institute of Electricaland Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),IEEE 802.20, or Evolved UTRA (E-UTRA). UTRA is part of a UniversalMobile Telecommunications System (UMTS). 3rd Generation PartnershipProject (3GPP) Long Term Evolution (LTE) is part of an Evolved UMTS(E-UMTS) using evolved UMTS Terrestrial Radio Access (E-UTRA), and itadopts OFDMA in downlink and adopts SC-FDMA in uplink. LTE-Advanced(LTE-A) is the evolution of 3GPP LTE.

Embodiments of the present invention may be supported by the standarddocuments disclosed in at least one of IEEE 802, 3GPP, and 3GPP2, thatis, radio access systems. That is, steps or portions that belong to theembodiments of the present invention and that are not described in orderto clearly expose the technical spirit of the present invention may besupported by the documents. Furthermore, all terms disclosed in thisdocument may be described by the standard documents.

In order to more clarify a description, 3GPP LTE/LTE-A is chieflydescribed, but the technical characteristics of the present inventionare not limited thereto.

General System to which the Present Invention May be Applied

FIG. 1 shows the structure of a radio frame in a wireless communicationsystem to which an embodiment of the present invention may be applied.

3GPP LTE/LTE-A support a radio frame structure type 1 which may beapplicable to Frequency Division Duplex (FDD) and a radio framestructure which may be applicable to Time Division Duplex (TDD).

The size of a radio frame in the time domain is represented as amultiple of a time unit of T_s=1/(15000*2048). A UL and DL transmissionincludes the radio frame having a duration of T_f=307200*T_s=10 ms.

FIG. 1(a) exemplifies a radio frame structure type 1. The type 1 radioframe may be applied to both of full duplex FDD and half duplex FDD.

A radio frame includes 10 subframes. A radio frame includes 20 slots ofT_slot=15360*T_s=0.5 ms length, and 0 to 19 indexes are given to each ofthe slots. One subframe includes consecutive two slots in the timedomain, and subframe i includes slot 2 i and slot 2 i+1. The timerequired for transmitting a subframe is referred to as a transmissiontime interval (TTI). For example, the length of the subframe i may be 1ms and the length of a slot may be 0.5 ms.

A UL transmission and a DL transmission I the FDD are distinguished inthe frequency domain. Whereas there is no restriction in the full duplexFDD, a UE may not transmit and receive simultaneously in the half duplexFDD operation.

One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols in the time domain and includes a pluralityof Resource Blocks (RBs) in a frequency domain. In 3GPP LTE, OFDMsymbols are used to represent one symbol period because OFDMA is used indownlink. An OFDM symbol may be called one SC-FDMA symbol or symbolperiod. An RB is a resource allocation unit and includes a plurality ofcontiguous subcarriers in one slot.

FIG. 1(b) shows frame structure type 2.

A type 2 radio frame includes two half frame of 153600*T_s=5 ms lengtheach. Each half frame includes 5 subframes of 30720*T_s=1 ms length.

In the frame structure type 2 of a TDD system, an uplink-downlinkconfiguration is a rule indicating whether uplink and downlink areallocated (or reserved) to all subframes.

Table 1 shows the uplink-downlink configuration.

TABLE 1 Downlink- to-Uplink Uplink- Switch- Downlink point Subframenumber configuration periodicity 0 1 2 3 4 5 6 7 8 9 0  5 ms D S U U U DS U U U 1  5 ms D S U U D D S U U D 2  5 ms D S U D D D S U D D 3 10 msD S U U U D D D D D 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D D DD D 6  5 ms D S U U U D S U U D

Referring to Table 1, in each subframe of the radio frame, ‘D’represents a subframe for a DL transmission, ‘U’ represents a subframefor UL transmission, and ‘S’ represents a special subframe includingthree types of fields including a Downlink Pilot Time Slot (DwPTS), aGuard Period (GP), and a Uplink Pilot Time Slot (UpPTS).

A DwPTS is used for an initial cell search, synchronization or channelestimation in a UE. A UpPTS is used for channel estimation in an eNB andfor synchronizing a UL transmission synchronization of a UE. A GP isduration for removing interference occurred in a UL owing to multi-pathdelay of a DL signal between a UL and a DL.

Each subframe i includes slot 2 i and slot 2 i+1 of T_slot=15360*T_s=0.5ms.

The UL-DL configuration may be classified into 7 types, and the positionand/or the number of a DL subframe, a special subframe and a UL subframeare different for each configuration.

Table 2 represents configuration (length of DwPTS/GP/UpPTS) of a specialsubframe.

TABLE 2 Normal cyclic prefix in Extended cyclic prefix downlink indownlink UpPTS UpPTS Normal Extended Normal Extended cyclic cycliccyclic cyclic prefix prefix prefix prefix Special subframe in in in inconfiguration DwPTS uplink uplink DwPTS uplink uplink 0  6592 · T_(s)2192 · T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 119760 · T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 ·T_(s) 25600 · T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 ·T_(s) 5  6592 · T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 ·T_(s) 23040 · T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

The structure of a radio subframe according to the example of FIG. 1 isjust an example, and the number of subcarriers included in a radioframe, the number of slots included in a subframe and the number of OFDMsymbols included in a slot may be changed in various manners.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin a wireless communication system to which an embodiment of the presentinvention may be applied.

Referring to FIG. 2, one downlink slot includes a plurality of OFDMsymbols in a time domain. It is described herein that one downlink slotincludes 7 OFDMA symbols and one resource block includes 12 subcarriersfor exemplary purposes only, and the present invention is not limitedthereto.

Each element on the resource grid is referred to as a resource element,and one resource block (RB) includes 12×7 resource elements. The numberof RBs NADL included in a downlink slot depends on a downlinktransmission bandwidth.

The structure of an uplink slot may be the same as that of a downlinkslot.

FIG. 3 shows the structure of a downlink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 3, a maximum of three OFDM symbols located in a frontportion of a first slot of a subframe correspond to a control region inwhich control channels are allocated, and the remaining OFDM symbolscorrespond to a data region in which a physical downlink shared channel(PDSCH) is allocated. Downlink control channels used in 3GPP LTEinclude, for example, a physical control format indicator channel(PCFICH), a physical downlink control channel (PDCCH), and a physicalhybrid-ARQ indicator channel (PHICH).

A PCFICH is transmitted in the first OFDM symbol of a subframe andcarries information about the number of OFDM symbols (i.e., the size ofa control region) which is used to transmit control channels within thesubframe. A PHICH is a response channel for uplink and carries anacknowledgement (ACK)/not-acknowledgement (NACK) signal for a HybridAutomatic Repeat Request (HARQ). Control information transmitted in aPDCCH is called Downlink Control Information (DCI). DCI includes uplinkresource allocation information, downlink resource allocationinformation, or an uplink transmission (Tx) power control command for aspecific UE group.

FIG. 4 shows the structure of an uplink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 4, the uplink subframe may be divided into a controlregion and a data region in a frequency domain. A physical uplinkcontrol channel (PUCCH) carrying uplink control information is allocatedto the control region. A physical uplink shared channel (PUSCH) carryinguser data is allocated to the data region. In order to maintain singlecarrier characteristic, one UE does not send a PUCCH and a PUSCH at thesame time.

A Resource Block (RB) pair is allocated to a PUCCH for one UE within asubframe. RBs belonging to an RB pair occupy different subcarriers ineach of 2 slots. This is called that an RB pair allocated to a PUCCH isfrequency-hopped in a slot boundary.

Multi-Input Multi-Output (MIMO)

A MIMO technology does not use single transmission antenna and singlereception antenna that have been commonly used so far, but uses amulti-transmission (Tx) antenna and a multi-reception (Rx) antenna. Inother words, the MIMO technology is a technology for increasing acapacity or enhancing performance using multi-input/output antennas inthe transmission end or reception end of a wireless communicationsystem. Hereinafter, MIMO is called a “multi-input/output antenna.”.

More specifically, the multi-input/output antenna technology does notdepend on a single antenna path in order to receive a single totalmessage and completes total data by collecting a plurality of datapieces received through several antennas. As a result, themulti-input/output antenna technology can increase a data transfer ratewithin a specific system range and can also increase a system rangethrough a specific data transfer rate.

It is expected that an efficient multi-input/output antenna technologywill be used because next-generation mobile communication requires adata transfer rate much higher than that of existing mobilecommunication. In such a situation, the MIMO communication technology isa next-generation mobile communication technology which may be widelyused in mobile communication UE and a relay node and has been in thespotlight as a technology which may overcome a limit to the transferrate of another mobile communication attributable to the expansion ofdata communication.

Meanwhile, the multi-input/output antenna (MIMO) technology of varioustransmission efficiency improvement technologies that are beingdeveloped has been most in the spotlight as a method capable ofsignificantly improving a communication capacity andtransmission/reception performance even without the allocation ofadditional frequencies or a power increase.

FIG. 5 shows the configuration of a known MIMO communication system.

Referring to FIG. 5, if the number of transmission (Tx) antennas isincreased to N_T and the number of reception (Rx) antennas is increasedto N_R at the same time, a theoretical channel transmission capacity isincreased in proportion to the number of antennas, unlike in the casewhere a plurality of antennas is used only in a transmitter or areceiver. Accordingly, a transfer rate can be improved, and frequencyefficiency can be significantly improved. In this case, a transfer rateaccording to an increase of a channel transmission capacity may betheoretically increased by a value obtained by multiplying the followingrate increment R_i by a maximum transfer rate R_o if one antenna isused.

R _(i)=min(N _(T) ,N _(R))  [Equation 1]

That is, in an MIMO communication system using 4 transmission antennasand 4 reception antennas, for example, a quadruple transfer rate can beobtained theoretically compared to a single antenna system.

Such a multi-input/output antenna technology may be divided into aspatial diversity method for increasing transmission reliability usingsymbols passing through various channel paths and a spatial multiplexingmethod for improving a transfer rate by sending a plurality of datasymbols at the same time using a plurality of transmission antennas.Furthermore, active research is being recently carried out on a methodfor properly obtaining the advantages of the two methods by combiningthe two methods.

Each of the methods is described in more detail below.

First, the spatial diversity method includes a space-time blockcode-series method and a space-time Trelis code-series method using adiversity gain and a coding gain at the same time. In general, theTrelis code-series method is better in terms of bit error rateimprovement performance and the degree of a code generation freedom,whereas the space-time block code-series method has low operationalcomplexity. Such a spatial diversity gain may correspond to an amountcorresponding to the product (N_T×N_R) of the number of transmissionantennas (N_T) and the number of reception antennas (N_R).

Second, the spatial multiplexing scheme is a method for sendingdifferent data streams in transmission antennas. In this case, in areceiver, mutual interference is generated between data transmitted by atransmitter at the same time. The receiver removes the interferenceusing a proper signal processing scheme and receives the data. A noiseremoval method used in this case may include a Maximum LikelihoodDetection (MLD) receiver, a Zero-Forcing (ZF) receiver, a Minimum MeanSquare Error (MMSE) receiver, Diagonal-Bell Laboratories LayeredSpace-Time (D-BLAST), and Vertical-Bell Laboratories Layered Space-Time(V-BLAST). In particular, if a transmission end can be aware of channelinformation, a Singular Value Decomposition (SVD) method may be used.

Third, there is a method using a combination of a spatial diversity andspatial multiplexing. If only a spatial diversity gain is to beobtained, a performance improvement gain according to an increase of adiversity disparity is gradually saturated. If only a spatialmultiplexing gain is used, transmission reliability in a radio channelis deteriorated. Methods for solving the problems and obtaining the twogains have been researched and may include a double space-time transmitdiversity (double-STTD) method and a space-time bit interleaved codedmodulation (STBICM).

In order to describe a communication method in a multi-input/outputantenna system, such as that described above, in more detail, thecommunication method may be represented as follows through mathematicalmodeling.

First, as shown in FIG. 5, it is assumed that N_T transmission antennasand NR reception antennas are present.

First, a transmission signal is described below. If the N_T transmissionantennas are present as described above, a maximum number of pieces ofinformation which can be transmitted are N_T, which may be representedusing the following vector.

s=└s ₁ ,s ₂ ,Λ,s _(N) _(T) ┘^(T)  [Equation 2]

Meanwhile, transmission power may be different in each of pieces oftransmission information s_1, s_2, . . . , s_NT. In this case, if piecesof transmission power are P_1, P_2, . . . , P_NT, transmissioninformation having controlled transmission power may be representedusing the following vector.

ŝ=[ŝ ₁ ,ŝ ₂ ,Λ,ŝ _(N) ^(T)]^(T)=[P ₁ s ₁ ,P ₂ s ₂ ,Λ,P _(N) _(T) ,s _(N)_(T) ]^(T)  [Equation 3]

Furthermore, transmission information having controlled transmissionpower in the Equation 3 may be represented as follows using the diagonalmatrix P of transmission power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & O & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\M \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \lbrack {{Equation}\mspace{14mu} 4} \rbrack\end{matrix}$

Meanwhile, the information vector having controlled transmission powerin the Equation 4 is multiplied by a weight matrix W, thus forming N_Ttransmission signals x_1, x_2, . . . , x_NT that are actuallytransmitted. In this case, the weight matrix functions to properlydistribute the transmission information to antennas according to atransport channel condition. The following may be represented using thetransmission signals x_1, x_2, . . . , x_NT.

$\begin{matrix}{x = {\lbrack \begin{matrix}x_{1} \\x_{2} \\M \\\begin{matrix}x_{i} \\\begin{matrix}M \\x_{N_{T}}\end{matrix}\end{matrix}\end{matrix} \rbrack = {{\begin{bmatrix}w_{11} & w_{12} & \Lambda & w_{1N_{T}} \\w_{21} & w_{22} & \Lambda & w_{2N_{T}} \\M & \; & O & \; \\w_{i\; 1} & w_{i\; 2} & \Lambda & w_{{iN}_{T}} \\M & \; & O & \; \\w_{N_{T}1} & w_{N_{T}2} & \Lambda & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\M \\{\hat{s}}_{j} \\M \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\hat{s}} = {WPs}}}}} & \lbrack {{Equation}\mspace{14mu} 5} \rbrack\end{matrix}$

In this case, w_ij denotes weight between the i-th transmission antennaand the j-th transmission information, and W is an expression of amatrix of the weight. Such a matrix W is called a weight matrix orprecoding matrix.

Meanwhile, the transmission signal x, such as that described above, maybe considered to be used in a case where a spatial diversity is used anda case where spatial multiplexing is used.

If spatial multiplexing is used, all the elements of the informationvector s have different values because different signals are multiplexedand transmitted. In contrast, if the spatial diversity is used, all theelements of the information vector s have the same value because thesame signals are transmitted through several channel paths.

A method of mixing spatial multiplexing and the spatial diversity may betaken into consideration. In other words, the same signals may betransmitted using the spatial diversity through 3 transmission antennas,for example, and the remaining different signals may be spatiallymultiplexed and transmitted.

If N_R reception antennas are present, the reception signals y_1, y_2, .. . , y_NR of the respective antennas are represented as follows using avector y.

y=[y ₁ ,y ₂ ,Λ,y _(N) _(R) ]^(T)  [Equation 6]

Meanwhile, if channels in a multi-input/output antenna communicationsystem are modeled, the channels may be classified according totransmission/reception antenna indices. A channel passing through areception antenna i from a transmission antenna j is represented ash_ij. In this case, it is to be noted that in order of the index ofh_ij, the index of a reception antenna comes first and the index of atransmission antenna then comes.

Several channels may be grouped and expressed in a vector and matrixform. For example, a vector expression is described below.

FIG. 6 is a diagram showing a channel from a plurality of transmissionantennas to a single reception antenna.

As shown in FIG. 6, a channel from a total of N_T transmission antennasto a reception antenna i may be represented as follows.

h _(i) ^(T) =└h _(i1) ,h _(i2) ,Λ,h _(iN) _(T) ┘  [Equation 7]

Furthermore, if all channels from the N_T transmission antenna to NRreception antennas are represented through a matrix expression, such asEquation 7, they may be represented as follows.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\M \\h_{i}^{T} \\M \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \Lambda & h_{1N_{T}} \\h_{21} & h_{22} & \Lambda & h_{2N_{T}} \\M & \; & O & \; \\h_{i\; 1} & h_{i\; 2} & \Lambda & h_{{iN}_{T}} \\M & \; & O & \; \\h_{N_{R}1} & h_{N_{R}2} & \Lambda & h_{N_{R}N_{T}}\end{bmatrix}}} & \lbrack {{Equation}\mspace{14mu} 8} \rbrack\end{matrix}$

Meanwhile, Additive White Gaussian Noise (AWGN) is added to an actualchannel after the actual channel experiences the channel matrix H.Accordingly, AWGN n_1, n_2, . . . , n_NR added to the N_R receptionantennas, respectively, are represented using a vector as follows.

n=[n ₁ ,n ₂ ,Λ,n _(N) _(R) ]^(T)  [Equation 9]

A transmission signal, a reception signal, a channel, and AWGN in amulti-input/output antenna communication system may be represented tohave the following relationship through the modeling of the transmissionsignal, reception signal, channel, and AWGN, such as those describedabove.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\M \\y_{i} \\M \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \Lambda & h_{1N_{T}} \\h_{21} & h_{22} & \Lambda & h_{2N_{T}} \\M & \; & O & \; \\h_{i\; 1} & h_{i\; 2} & \Lambda & h_{{iN}_{T}} \\M & \; & O & \; \\h_{N_{R}1} & h_{N_{R}2} & \Lambda & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\M \\x_{j} \\M \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\M \\\begin{matrix}n_{i} \\\begin{matrix}M \\n_{N_{R}}\end{matrix}\end{matrix}\end{bmatrix}} = {{Hx} + n}}}} & \lbrack {{Equation}\mspace{14mu} 10} \rbrack\end{matrix}$

Meanwhile, the number of rows and columns of the channel matrix Hindicative of the state of channels is determined by the number oftransmission/reception antennas. In the channel matrix H, as describedabove, the number of rows becomes equal to the number of receptionantennas N_R, and the number of columns becomes equal to the number oftransmission antennas N_T. That is, the channel matrix H becomes anN_R×N_T matrix.

In general, the rank of a matrix is defined as a minimum number of thenumber of independent rows or columns. Accordingly, the rank of thematrix is not greater than the number of rows or columns. As for figuralstyle, for example, the rank H of the channel matrix H is limited asfollows.

rank(H)>min(N _(T) ,N _(R))  [Equation 11]

Furthermore, if a matrix is subjected to Eigen value decomposition, arank may be defined as the number of Eigen values that belong to Eigenvalues and that are not 0. Likewise, if a rank is subjected to SingularValue Decomposition (SVD), it may be defined as the number of singularvalues other than 0. Accordingly, the physical meaning of a rank in achannel matrix may be said to be a maximum number on which differentinformation may be transmitted in a given channel.

In this specification, a “rank” for MIMO transmission indicates thenumber of paths through which signals may be independently transmittedat a specific point of time and a specific frequency resource. The“number of layers” indicates the number of signal streams transmittedthrough each path. In general, a rank has the same meaning as the numberof layers unless otherwise described because a transmission end sendsthe number of layers corresponding to the number of ranks used in signaltransmission.

Reference Signal (RS)

In a wireless communication system, a signal may be distorted duringtransmission because data is transmitted through a radio channel. Inorder for a reception end to accurately receive a distorted signal, thedistortion of a received signal needs to be corrected using channelinformation. In order to detect channel information, a method ofdetecting channel information using the degree of the distortion of asignal transmission method and a signal known to both the transmissionside and the reception side when they are transmitted through a channelis chiefly used. The aforementioned signal is called a pilot signal orreference signal (RS).

Furthermore recently, when most of mobile communication systems transmita packet, they use a method capable of improving transmission/receptiondata efficiency by adopting multiple transmission antennas and multiplereception antennas instead of using one transmission antenna and onereception antenna used so far. When data is transmitted and receivedusing multiple input/output antennas, a channel state between thetransmission antenna and the reception antenna must be detected in orderto accurately receive the signal. Accordingly, each transmission antennamust have an individual reference signal.

In a mobile communication system, an RS may be basically divided intotwo types depending on its object. There are an RS having an object ofobtaining channel state information and an RS used for datademodulation. The former has an object of obtaining, by a UE, to obtainchannel state information in the downlink. Accordingly, a correspondingRS must be transmitted in a wideband, and a UE must be capable ofreceiving and measuring the RS although the UE does not receive downlinkdata in a specific subframe. Furthermore, the former is also used forradio resources management (RRM) measurement, such as handover. Thelatter is an RS transmitted along with corresponding resources when aneNB transmits the downlink. A UE may perform channel estimation byreceiving a corresponding RS and thus may demodulate data. Thecorresponding RS must be transmitted in a region in which data istransmitted.

A downlink RS includes one common RS (CRS) for the acquisition ofinformation about a channel state shared by all of UEs within a cell andmeasurement, such as handover, and a dedicated RS (DRS) used for datademodulation for only a specific UE. Information for demodulation andchannel measurement can be provided using such RSs. That is, the DRS isused for only data demodulation, and the CRS is used for the two objectsof channel information acquisition and data demodulation.

The reception side (i.e., UE) measures a channel state based on a CRSand feeds an indicator related to channel quality, such as a channelquality indicator (CQI), a precoding matrix index (PMI) and/or a rankindicator (RI), back to the transmission side (i.e., an eNB). The CRS isalso called a cell-specific RS. In contrast, a reference signal relatedto the feedback of channel state information (CSI) may be defined as aCSI-RS.

The DRS may be transmitted through resource elements if data on a PDSCHneeds to be demodulated. A UE may receive information about whether aDRS is present through a higher layer, and the DRS is valid only if acorresponding PDSCH has been mapped. The DRS may also be called aUE-specific RS or demodulation RS (DMRS).

FIG. 7 illustrates reference signal patterns mapped to downlink resourceblock pairs in a wireless communication system to which the presentinvention may be applied.

Referring to FIG. 7, a downlink resource block pair, that is, a unit inwhich a reference signal is mapped, may be represented in the form ofone subframe in a time domain X 12 subcarriers in a frequency domain.That is, in a time axis (an x axis), one resource block pair has alength of 14 OFDM symbols in the case of a normal cyclic prefix (CP)(FIG. 7a ) and has a length of 12 OFDM symbols in the case of anextended cyclic prefix (CP) (FIG. 7b ). In the resource block lattice,resource elements (REs) indicated by “0”, “1”, “2”, and “3” mean thelocations of the CRSs of antenna port indices “0”, “1”, “2”, and “3”,respectively, and REs indicated by “D” mean the location of a DRS.

If an eNB uses a single transmission antenna, reference signals for asingle antenna port are arrayed.

If an eNB uses two transmission antennas, reference signals for twotransmission antenna ports are arrayed using a time divisionmultiplexing (TDM) scheme and/or a frequency division multiplexing (FDM)scheme. That is, different time resources and/or different frequencyresources are allocated in order to distinguish between referencesignals for two antenna ports.

Furthermore, if an eNB uses four transmission antennas, referencesignals for four transmission antenna ports are arrayed using the TDMand/or FDM schemes. Channel information measured by the reception side(i.e., UE) of a downlink signal may be used to demodulate datatransmitted using a transmission scheme, such as single transmissionantenna transmission, transmission diversity, closed-loop spatialmultiplexing, open-loop spatial multiplexing or amulti-user-multi-input/output (MIMO) antenna.

If a multi-input multi-output antenna is supported, when a RS istransmitted by a specific antenna port, the RS is transmitted in thelocations of resource elements specified depending on a pattern of theRS and is not transmitted in the locations of resource elementsspecified for other antenna ports. That is, RSs between differentantennas do not overlap.

In an LTE-A system, that is, an advanced and developed form of the LTEsystem, the design is necessary to support a maximum of eighttransmission antennas in the downlink of an eNB. Accordingly, RSs forthe maximum of eight transmission antennas must be also supported. Inthe LTE system, only downlink RSs for a maximum of four antenna portshas been defined. Accordingly, if an eNB has four to a maximum of eightdownlink transmission antennas in the LTE-A system, RSs for theseantenna ports must be additionally defined and designed. Regarding theRSs for the maximum of eight transmission antenna ports, theaforementioned RS for channel measurement and the aforementioned RS fordata demodulation must be designed.

One of important factors that must be considered in designing an LTE-Asystem is backward compatibility, that is, that an LTE UE must welloperate even in the LTE-A system, which must be supported by the system.From an RS transmission viewpoint, in the time-frequency domain in whicha CRS defined in LTE is transmitted in a full band every subframe, RSsfor a maximum of eight transmission antenna ports must be additionallydefined. In the LTE-A system, if an RS pattern for a maximum of eighttransmission antennas is added in a full band every subframe using thesame method as the CRS of the existing LTE, RS overhead is excessivelyincreased.

Accordingly, the RS newly designed in the LTE-A system is basicallydivided into two types, which include an RS having a channel measurementobject for the selection of MCS or a PMI (channel state information-RSor channel state indication-RS (CSI-RS)) and an RS for the demodulationof data transmitted through eight transmission antennas (datademodulation-RS (DM-RS)).

The CSI-RS for the channel measurement object is characterized in thatit is designed for an object focused on channel measurement unlike theexisting CRS used for objects for measurement, such as channelmeasurement and handover, and for data demodulation. Furthermore, theCSI-RS may also be used for an object for measurement, such as handover.The CSI-RS does not need to be transmitted every subframe unlike the CRSbecause it is transmitted for an object of obtaining information about achannel state. In order to reduce overhead of a CSI-RS, the CSI-RS isintermittently transmitted on the time axis.

In the LTE-A system, a maximum of eight transmission antennas aresupported in the downlink of an eNB. In the LTE-A system, if RSs for amaximum of eight transmission antennas are transmitted in a full bandevery subframe using the same method as the CRS in the existing LTE, RSoverhead is excessively increased. Accordingly, in the LTE-A system, anRS has been separated into the CSI-RS of the CSI measurement object forthe selection of MCS or a PMI and the DM-RS for data demodulation, andthus the two RSs have been added. The CSI-RS may also be used for anobject, such as RRM measurement, but has been designed for a main objectfor the acquisition of CSI. The CSI-RS does not need to be transmittedevery subframe because it is not used for data demodulation.Accordingly, in order to reduce overhead of the CSI-RS, the CSI-RS isintermittently transmitted on the time axis. That is, the CSI-RS has aperiod corresponding to a multiple of the integer of one subframe andmay be periodically transmitted or transmitted in a specifictransmission pattern. In this case, the period or pattern in which theCSI-RS is transmitted may be set by an eNB.

In order to measure a CSI-RS, a UE must be aware of information aboutthe transmission subframe index of the CSI-RS for each CSI-RS antennaport of a cell to which the UE belongs, the location of a CSI-RSresource element (RE) time-frequency within a transmission subframe, anda CSI-RS sequence.

In the LTE-A system, an eNB has to transmit a CSI-RS for each of amaximum of eight antenna ports. Resources used for the CSI-RStransmission of different antenna ports must be orthogonal. When one eNBtransmits CSI-RSs for different antenna ports, it may orthogonallyallocate the resources according to the FDM/TDM scheme by mapping theCSI-RSs for the respective antenna ports to different REs.Alternatively, the CSI-RSs for different antenna ports may betransmitted according to the CDM scheme for mapping the CSI-RSs topieces of code orthogonal to each other.

When an eNB notifies a UE belonging to the eNB of information on aCSI-RS, first, the eNB must notify the UE of information about atime-frequency in which a CSI-RS for each antenna port is mapped.Specifically, the information includes subframe numbers in which theCSI-RS is transmitted or a period in which the CSI-RS is transmitted, asubframe offset in which the CSI-RS is transmitted, an OFDM symbolnumber in which the CSI-RS RE of a specific antenna is transmitted,frequency spacing, and the offset or shift value of an RE in thefrequency axis.

A CSI-RS is transmitted through one, two, four or eight antenna ports.Antenna ports used in this case are p=15, p=15, 16, p=15, . . . , 18,and p=15, . . . , 22, respectively. A CSI-RS may be defined for only asubcarrier interval Δf=15 kHz.

In a subframe configured for CSI-RS transmission, a CSI-RS sequence ismapped to a complex-valued modulation symbol a_k,l{circumflex over( )}(p) used as a reference symbol on each antenna port p as in Equation12.

                                     [Equation  12]     a_(k, l)^((p)) = w_(l^(″)) ⋅ r_(l, n_(s))(m^(′))$\mspace{79mu} {k = {k^{\prime} + {12m} + \{ {{\begin{matrix}{- 0} & {{{{for}\mspace{11mu} p} \in \{ {15,16} \}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 6} & {{{{for}\mspace{11mu} p} \in \{ {17,18} \}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 1} & {{{{for}\mspace{11mu} p} \in \{ {19,20} \}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 7} & {{{{for}\mspace{11mu} p} \in \{ {21,22} \}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 0} & {{{{for}\mspace{11mu} p} \in \{ {15,16} \}},{{extended}\mspace{11mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 3} & {{{{for}\mspace{11mu} p} \in \{ {17,18} \}},{{extended}\mspace{11mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 6} & {{{{for}\mspace{11mu} p} \in \{ {19,20} \}},{{extended}\mspace{11mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 9} & {{{{for}\mspace{11mu} p} \in \{ {21,22} \}},{{extended}\mspace{11mu} {cyclic}\mspace{14mu} {prefix}}}\end{matrix}l} = {l^{\prime} + \{ {{\begin{matrix}l^{''} & {{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{14mu} {configurations}\mspace{14mu} 0\text{-}19},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{2l^{''}} & {{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{14mu} {configurations}\mspace{14mu} 20\text{-}31},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\l^{''} & {{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{14mu} {configurations}\mspace{14mu} 0\text{-}27},{{extended}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}}\end{matrix}\mspace{79mu} w_{l^{''}}} = \{ {{{\begin{matrix}1 & {p \in \{ {15,17,19,21} \}} \\( {- 1} )^{l^{''}} & {p \in \{ {16,18,20,22} \}}\end{matrix}\mspace{79mu} l^{''}} = 0},{{1\mspace{79mu} m} = 0},1,\ldots \mspace{11mu},{{N_{RB}^{DL} - {1\mspace{79mu} m^{\prime}}} = {m + \lfloor \frac{N_{RB}^{\max,{DL}} - N_{RB}^{DL}}{2} \rfloor}}} } }} }}$

In Equation 12, (k′,l′) (wherein k′ is a subcarrier index within aresource block and l′ indicates an OFDM symbol index within a slot.) andthe condition of n_s is determined depending on a CSI-RS configuration,such as Table 3 or Table 4.

Table 3 illustrates the mapping of (k′,l′) from a CSI-RS configurationin a normal CP.

TABLE 3 Number of CSI reference signals CSI reference configured signal1 or 2 4 8 configuration (k′, l′) n_(s) mod2 (k′, l′) n_(s) mod2 (k′,l′) n_(s) mod2 Frame structure type 1 and 2 0 (9, 5) 0 (9, 5) 0 (9, 5) 01 (11, 2) 1 (11, 2) 1 (11, 2) 1 2 (9, 2) 1 (9, 2) 1 (9, 2) 1 3 (7, 2) 1(7, 2) 1 (7, 2) 1 4 (9, 5) 1 (9, 5) 1 (9, 5) 1 5 (8, 5) 0 (8, 5) 0 6(10, 2) 1 (10, 2) 1 7 (8, 2) 1 (8, 2) 1 8 (6, 2) 1 (6, 2) 1 9 (8, 5) 1(8, 5) 1 10 (3, 5) 0 11 (2, 5) 0 12 (5, 2) 1 13 (4, 2) 1 14 (3, 2) 1 15(2, 2) 1 16 (1, 2) 1 17 (0, 2) 1 18 (3, 5) 1 19 (2, 5) 1 Frame structuretype 2 only 20 (11, 1) 1 (11, 1) 1 (11, 1) 1 21 (9, 1) 1 (9, 1) 1 (9, 1)1 22 (7, 1) 1 (7, 1) 1 (7, 1) 1 23 (10, 1) 1 (10, 1) 1 24 (8, 1) 1(8, 1) 1 25 (6, 1) 1 (6, 1) 1 26 (5, 1) 1 27 (4, 1) 1 28 (3, 1) 1 29(2, 1) 1 30 (1, 1) 1 31 (0, 1) 1

Table 4 illustrates the mapping of (k′,l′) from a CSI-RS configurationin an extended CP.

TABLE 4 Number of CSI reference signals CSI reference configured signal1 or 2 4 8 configuration (k′, l′) n_(s) mod2 (k′, l′) n_(s) mod2 (k′,l′) n_(s) mod2 Frame structure type 1 and 2 0 (11, 4) 0 (11, 4) 0 (11,4) 0 1 (9, 4) 0 (9, 4) 0 (9, 4) 0 2 (10, 4) 1 (10, 4) 1 (10, 4) 1 3 (9,4) 1 (9, 4) 1 (9, 4) 1 4 (5, 4) 0 (5, 4) 0 5 (3, 4) 0 (3, 4) 0 6 (4, 4)1 (4, 4) 1 7 (3, 4) 1 (3, 4) 1 8 (8, 4) 0 9 (6, 4) 0 10 (2, 4) 0 11 (0,4) 0 12 (7, 4) 1 13 (6, 4) 1 14 (1, 4) 1 15 (0, 4) 1 Frame structuretype 16 (11, 1) 1 (11, 1) 1 (11, 1) 1 17 (10, 1) 1 (10, 1) 1 (10, 1) 118 (9, 1) 1 (9, 1) 1 (9, 1) 1 19 (5, 1) 1 (5, 1) 1 20 (4, 1) 1 (4, 1) 121 (3, 1) 1 (3, 1) 1 22 (8, 1) 1 23 (7, 1) 1 24 (6, 1) 1 25 (2, 1) 1 26(1, 1) 1 27 (0, 1) 1

Referring to Table 3 and Table 4, in the transmission of a CSI-RS, inorder to reduce inter-cell interference (ICI) in a multi-cellenvironment including a heterogeneous network (HetNet) environment, amaximum of 32 different configurations (in the case of a normal CP) or amaximum of 28 different configurations (in the case of an extended CP)are defined.

The CSI-RS configuration is different depending on the number of antennaports and a CP within a cell, and a neighboring cell may have a maximumof different configurations. Furthermore, the CSI-RS configuration maybe divided into a case where it is applied to both an FDD frame and aTDD frame and a case where it is applied to only a TDD frame dependingon a frame structure.

(k′,l′) and n_s are determined depending on a CSI-RS configuration basedon Table 3 and Table 4, and time-frequency resources used for CSI-RStransmission are determined depending on each CSI-RS antenna port.

FIG. 8 is a diagram illustrating resources to which reference signalsare mapped in a wireless communication system to which the presentinvention may be applied. Particularly, FIG. 8 illustrates CSI-RSpatterns for cases in which the number of CSI-RS antenna ports is 1 or2, 4 and 8 in a subframe to which a normal CP is applied.

FIG. 8(a) shows twenty types of CSI-RS configurations available forCSI-RS transmission by one or two CSI-RS antenna ports, FIG. 8(b) showsten types of CSI-RS configurations available for four CSI-RS antennaports, and FIG. 8(c) shows five types of CSI-RS configurations availablefor eight CSI-RS antenna ports.

As described above, radio resources (i.e., an RE pair) in which a CSI-RSis transmitted are determined depending on each CSI-RS configuration.

If one or two antenna ports are configured for CSI-RS transmission withrespect to a specific cell, the CSI-RS is transmitted on radio resourceson a configured CSI-RS configuration of the twenty types of CSI-RSconfigurations shown in FIG. 8(a).

Likewise, when four antenna ports are configured for CSI-RS transmissionwith respect to a specific cell, a CSI-RS is transmitted on radioresources on a configured CSI-RS configuration of the ten types ofCSI-RS configurations shown in FIG. 8(b). Furthermore, when eightantenna ports are configured for CSI-RS transmission with respect to aspecific cell, a CSI-RS is transmitted on radio resources on aconfigured CSI-RS configuration of the five types of CSI-RSconfigurations shown in FIG. 8(c).

A CSI-RS for each antenna port is subjected to CDM(Code DivisionMultiplexing) for every two antenna ports (i.e., {15,16}, {17,18},{19,20} and {21,22}) on the same radio resources and transmitted. Forexample, in the case of antenna ports 15 and 16, CSI-RS complex symbolsfor the respective antenna ports 15 and 16 are the same, but aremultiplied by different types of orthogonal code (e.g., Walsh code) andmapped to the same radio resources. The complex symbol of the CSI-RS forthe antenna port 15 is multiplied by [1, 1], and the complex symbol ofthe CSI-RS for the antenna port 16 is multiplied by [1 −1] and mapped tothe same radio resources. The same is true of the antenna ports {17,18},{19,20} and {21,22}.

A UE may detect a CSI-RS for a specific antenna port by multiplying codeby which a transmitted symbol has been multiplied. That is, atransmitted symbol is multiplied by the code [1 1] multiplied in orderto detect the CSI-RS for the antenna port 15, and a transmitted symbolis multiplied by the code [1 −1] multiplied in order to detect theCSI-RS for the antenna port 16.

Referring to FIGS. 8(a) to 8(c), in the case of the same CSI-RSconfiguration index, radio resources according to a CSI-RS configurationhaving a large number of antenna ports include radio resources having asmall number of CSI-RS antenna ports. For example, in the case of aCSI-RS configuration 0, radio resources for the number of eight antennaports include both radio resources for the number of four antenna portsand radio resources for the number of one or two antenna ports.

FIG. 9 illustrates resources to which reference signals are mapped in awireless communication system to which the present invention isapplicable.

Particularly, FIG. 9 shows CSI-RS patterns for cases in which the numberof CSI-RS antenna ports is 1 or 2, 4 and 8 in a subframe to which anextended CP is applied.

FIG. 9(a) shows 16 CSI-RS configurations which can be used for CSI-RStransmission through 1 or 2 CSI-RS antenna ports, FIG. 9(b) shows 8CSI-RS configurations which can be used for CSI-RS transmission through4 CSI-RS antenna ports, and FIG. 9(c) shows 4 CSI-RS configurationswhich can be used for CSI-RS transmission through 8 CSI-RS antennaports.

In this manner, radio resources (i.e., RE pairs) for CSI-RS transmissionare determined depending on each CSI-RS configuration.

When one or two antenna ports are set for CSI-RS transmission for aspecific cell, CSI-RSs are transmitted on radio resources according to aset CSI-RS configuration among the 16 CSI-RS configurations shown inFIG. 9(a).

Similarly, when 4 antenna ports are set for CSI-RS transmission for aspecific cell, CSI-RSs are transmitted on radio resources according to aset CSI-RS configuration among the 8 CSI-RS configurations shown in FIG.9(b). Further, when 8 antenna ports are set for CSI-RS transmission fora specific cell, CSI-RSs are transmitted on radio resources according toa set CSI-RS configuration among the 4 CSI-RS configurations shown inFIG. 9(c). A plurality of CSI-RS configurations may be used in a singlecell. Only zero or one CSI-RS configuration may be used for a non-zeropower (NZP) CSI-RS and zero or multiple CSI-RS configurations may beused for a zero power (ZP) CSI-RS.

For each bit set to 1 in a zero-power (ZP) CSI-RS (‘ZeroPowerCSI-RS)that is a bitmap of 16 bits configured by a high layer, a UE assumeszero transmission power in REs (except a case where an RE overlaps an REassuming a NZP CSI-RS configured by a high layer) corresponding to thefour CSI-RS columns of Table 3 and Table 4. The most significant bit(MSB) corresponds to the lowest CSI-RS configuration index, and nextbits in the bitmap sequentially correspond to next CSI-RS configurationindices.

A CSI-RS is transmitted only in a downlink slot that satisfies thecondition of (n_s mod 2) in Table 3 and Table 4 and a subframe thatsatisfies the CSI-RS subframe configurations.

In the case of the frame structure type 2 (TDD), a CSI-RS is nottransmitted in a special subframe, a synchronization signal (SS), asubframe colliding against a PBCH or SystemInformationBlockType1 (SIB 1)Message transmission or a subframe configured to paging messagetransmission.

Furthermore, an RE in which a CSI-RS for any antenna port belonging toan antenna port set S (S={15}, S={15,16}, S={17,18}, 5={19,20} orS={21,22}) is transmitted is not used for the transmission of a PDSCH orfor the CSI-RS transmission of another antenna port.

Time-frequency resources used for CSI-RS transmission cannot be used fordata transmission. Accordingly, data throughput is reduced as CSI-RSoverhead is increased. By considering this, a CSI-RS is not configuredto be transmitted every subframe, but is configured to be transmitted ineach transmission period corresponding to a plurality of subframes. Inthis case, CSI-RS transmission overhead can be significantly reducedcompared to a case where a CSI-RS is transmitted every subframe.

A subframe period (hereinafter referred to as a “CSI transmissionperiod”) T_CSI-RS and a subframe offset Δ_CSI-RS for CSI-RS transmissionare shown in Table 5.

Table 5 illustrates CSI-RS subframe configurations.

TABLE 5 CSI-RS CSI-RS periodicity subframe CSI-RS-SubframeConfigT_(CSI-RS) offset Δ_(CSI-RS) I_(CSI-RS) (subframes) (subframes) 0-4  5I_(CSI-RS)  5-14 10 I_(CSI-RS)-5 15-34 20 I_(CSI-RS)-15 35-74 40I_(CSI-RS)-35  75-154 80 I_(CSI-RS)-75

Referring to Table 5, CSI-RS periodicity TCSI-RS and a subframe offsetΔCSI-RS are determined depending on CSI-RS subframe configurationICSI-RS.

The CSI-RS subframe configuration in Table 5 may be set to one of theaforementioned ‘SubframeConfig’ field and ‘zeroTxPowerSubframeConfig’field. The CSI-RS subframe configuration may be separately set for anNZP CSI-RS and a ZP CSI-RS.

A subframe including a CSI-RS satisfies Equation 13.

(10n _(f) +└n _(s)/2┘−Δ_(CSI-RS))mod T _(CSI-RS)=0  [Equation 13]

In Equation 13, TCSI-RS indicates CSI-RS periodicity, ΔCSI-RS indicatesa subframe offset value, of denotes a system frame number, and nsdenotes a slot number.

In the case of a UE for which transmission mode 9 is set with respect toa serving cell, a single CSI-RS resource configuration may be set forthe UE. In the case of a UE for which transmission mode 10 is set withrespect to the serving cell, one or more CSI-RS resource configurationsmay be set for the UE.

CSI-RS Configuration

In the current LTE standard, CSI-RS configuration parameters includeantennaPortsCount, subframeConfig, resourceConfig, etc. These parametersindicate the number of antenna ports used to transmit CSI-RS, the periodand offset of a subframe for transmitting CSI-RS, and a transmitted RElocation (frequency and OFDM symbol index) in the correspondingsubframe. Particularly, when a base station delivers specific CSI-RSconfiguration to a UE, it delivers the following parameters/information.

-   -   antennaPortsCount: A parameter representing the number of        antenna ports used for transmission of CSI reference signals        (e.g., 1 CSI-RS port, 2 CSI-RS ports, 4 CSI-RS ports, 8 CSI-RS        ports, etc.).    -   resourceConfig: A parameter associated with the location of        resources allocated for CSI-RS.    -   subframeConfig: A parameter associated with the period and        offset of a subframe for transmitting CSI-RS.    -   p-C: Regarding UE assumption on reference PDSCH transmitted        power for CSI feedback CSI-RS, Pc is the assumed ratio of PDSCH        EPRE to CSI-RS EPRE when UE derives CSI feedback and takes        values in the range of [−8, 15] dB with 1 dB step size.    -   zeroTxPowerResourceConfigList: A parameter associated with        zero-power CSI-RS configuration.    -   zeroTxPowerSubframeConfig: A parameter associated with the        period and offset of a subframe for transmitting zero-power        CSI-RS.

Massive MIMO

A MIMO system having a plurality of antennas may be called a massiveMIMO system and attracts attention as a means for improving spectralefficiency, energy efficiency and processing complexity.

Recently, the massive MIMO system has been discussed in order to meetrequirements for spectral efficiency of future mobile communicationsystems in 3GPP. Massive MIMO is also called full-dimension MIMO(FD-MIMO).

LTE release-12 and following wireless communication systems considerintroduction of an active antenna system (AAS).

Distinguished from conventional passive antenna systems in which anamplifier capable of adjusting the phase and magnitude of a signal isseparated from an antenna, the AAS is configured in such a manner thateach antenna includes an active element such as an amplifier.

The AAS does not require additional cables, connectors and hardware forconnecting amplifiers and antennas and thus has high energy efficiencyand low operation costs. Particularly, the AAS supports electronic beamcontrol per antenna and thus can realize enhanced MIMO for formingaccurate beam patterns in consideration of a beam direction and a beamwidth or 3D beam patterns.

With the introduction of enhanced antenna systems such as the AAS,massive MIMO having a plurality of input/output antennas and amulti-dimensional antenna structure is also considered. For example,when a 2D antenna array instead of a conventional linear antenna arrayis formed, a 3D beam pattern can be formed using active antennas of theAAS.

FIG. 10 illustrates a 2D AAS having 64 antenna elements in a wirelesscommunication system to which the present invention is applicable.

FIG. 10 illustrates a normal 2D antenna array. A case in which Nt=Nv·Nhantennas are arranged in a square form, as shown in FIG. 10, may beconsidered. Here, Nh indicates the number of antenna columns in thehorizontal direction and Nv indicates the number of antenna rows in thevertical direction.

When the aforementioned 2D antenna array is used, radio waves can becontrolled in both the vertical direction (elevation) and the horizontaldirection (azimuth) to control transmitted beams in a 3D space. Awavelength control mechanism of this type may be referred to as 3Dbeamforming.

FIG. 11 illustrates a system in which an eNB or a UE has a plurality oftransmission/reception antennas capable of forming AAS based 3D beams ina wireless communication system to which the present invention isapplicable.

FIG. 11 schematizes the above-described example and illustrates a 3DMIMO system using a 2D antenna array (i.e., 2D-AAS).

From the viewpoint of transmission antennas, quasi-static or dynamicbeam formation in the vertical direction as well as the horizontaldirection of beams can be performed when a 3D beam pattern is used. Forexample, application such as sector formation in the vertical directionmay be considered.

From the viewpoint of reception antennas, a signal power increase effectaccording to an antenna array gain can be expected when a received beamis formed using a massive reception antenna. Accordingly, in the case ofuplink, an eNB can receive signals transmitted from a UE through aplurality of antennas, and the UE can set transmission power thereof toa very low level in consideration of the gain of the massive receptionantenna.

FIG. 12 illustrates a 2D antenna system having cross polarization in awireless communication system to which the present invention isapplicable.

2D planar antenna array model considering polarization may beschematized as shown in FIG. 12.

Distinguished from conventional MIMO systems using passive antennas,systems based on active antennas can dynamically control gains ofantenna elements by applying a weight to an active element (e.g.,amplifier) attached to (or included in) each antenna element. Since aradiation pattern depends on antenna arrangement such as the number ofantenna elements and antenna spacing, an antenna system can be modeledat an antenna element level.

The antenna arrangement model as shown in FIG. 12 may be represented by(M, N, P) which corresponds to parameters characterizing an antennaarrangement structure.

M indicates the number of antenna elements having the same polarizationin each column (i.e., in the vertical direction) (i.e., the number ofantenna elements having +45° slant in each column or the number ofantenna elements having −45° slant in each column).

N indicates the number of columns in the horizontal direction (i.e., thenumber of antenna elements in the horizontal direction).

P indicates the number of dimensions of polarization. P=2 in the case ofcross polarization as shown in FIG. 11, whereas P=1 in the case ofco-polarization.

An antenna port may be mapped to a physical antenna element. The antennaport may be defined by a reference signal associated therewith. Forexample, antenna port 0 may be associated with a cell-specific referencesignal (CRS) and antenna port 6 may be associated with a positioningreference signal (PRS) in the LTE system.

For example, antenna ports and physical antenna elements may beone-to-one mapped. This may correspond to a case in which a singlecross-polarization antenna element is used for downlink MIMO or downlinktransmit diversity. For example, antenna port 0 may be mapped to asingle physical antenna element, whereas antenna port 1 may be mapped toanother physical antenna element. In this case, two downlinktransmissions are present in terms of a UE. One is associated with areference signal for antenna port 0 and the other is associated with areference signal for antenna port 1.

Alternatively, a single antenna port may be mapped to multiple physicalantenna elements. This may correspond to a case in which a singleantenna port is used for beamforming. Beamforming can cause downlinktransmission to be directed to a specific UE by using multiple physicalantenna elements. This can be accomplished using an antenna arraycomposed of multiple columns of multiple cross-polarization antennaelements in general. In this case, a single downlink transmissionderived from a single antenna port is present in terms of a UE. One isassociated with a CRS for antenna port 0 and the other is associatedwith a CRS for antenna port 1.

That is, an antenna port represents downlink transmission in terms of aUE rather than substantial downlink transmission from a physical antennaelement in an eNB.

Alternatively, a plurality of antenna ports may be used for downlinktransmission and each antenna port may be multiple physical antennaports. This may correspond to a case in which antenna arrangement isused for downlink MIMO or downlink diversity. For example, antenna port0 may be mapped to multiple physical antenna ports and antenna port 1may be mapped to multiple physical antenna ports. In this case, twodownlink transmissions are present in terms of a UE. One is associatedwith a reference signal for antenna port 0 and the other is associatedwith a reference signal for antenna port 1.

In FD-MIMO, MIMO precoding of a data stream may be subjected to antennaport virtualization, transceiver unit (TXRU) virtualization and anantenna element pattern.

In antenna port virtualization, a stream on an antenna port is precodedon TXRU. In TXRU virtualization, a TXRU signal is precoded on an antennaelement. In the antenna element pattern, a signal radiated from anantenna element may have a directional gain pattern.

In conventional transceiver modeling, static one-to-on mapping betweenan antenna port and TXRU is assumed and TXRU virtualization effect isintegrated into a (TXRU) antenna pattern including both the effects ofthe TXRU virtualization and antenna element pattern.

Antenna port virtualization may be performed through afrequency-selective method. In LTE, an antenna port is defined alongwith a reference signal (or pilot). For example, for transmission ofdata precoded on an antenna port, a DMRS is transmitted in the samebandwidth as that for a data signal and both the DMRS and the datasignal are precoded through the same precoder (or the same TXRUvirtualization precoding). For CSI measurement, a CSI-RS is transmittedthrough multiple antenna ports. In CSI-RS transmission, a precoder whichcharacterizes mapping between a CSI-RS port and TXRU may be designed asan eigen matrix such that a UE can estimate a TXRU virtualizationprecoding matrix for a data precoding vector.

1D TXRU virtualization and 2D TXRU virtualization are discussed as TXRUvirtualization methods, which will be described below with reference tothe drawings.

FIG. 13 illustrates transceiver unit models in a wireless communicationsystem to which the present invention is applicable.

In 1D TXRU virtualization, M_TXRU TXRUs are associated with M antennaelements in a single-column antenna arrangement having the samepolarization.

In 2D TXRU virtualization, a TXRU model corresponding to the antennaarrangement model (M, N, P) of FIG. 12 may be represented by (M_TXRU, N,P). Here, M_TXRU denotes the number of 2D TXRUs present in the samecolumn and the same polarization, and M_TXRU≤M all the time. That is, atotal number of TXRUs is M_TXRU×N×P.

TXRU virtualization models may be divided into TXRU virtualization modeloption-1: sub-array partition model as shown in FIG. 12(a) and TXRUvirtualization model option-2: full-connection model as shown in FIG.12(b) according to correlation between antenna elements and TXRU.

Referring to FIG. 13(a), antenna elements are partitioned into multipleantenna element groups and each TXRU is connected to one of the groupsin the case of the sub-array partition model.

Referring to FIG. 13(b), multiple TXRU signals are combined anddelivered to a single antenna element (or antenna element array) in thecase of the full-connection model.

In FIG. 13, q is a transmission signal vector of M co-polarized antennaelements in a single column, w is a wideband TXRU virtualization weightvector, W is a wideband TXRU virtualization weight matrix, and x is asignal vector of M_TXRU TXRUs.

Here, mapping between antenna ports and TXRUs may be 1-to-1 or 1-to-manymapping.

FIG. 13 shows an example of TXRU-to-antenna element mapping and thepresent invention is not limited thereto. The present invention may beequally applied to mapping between TXRUs and antenna elements realizedin various manners in terms of hardware.

Definition of CSI(Channel-State Information)—Reference Signal(CSI-RS)

For a serving cell and UE configured in transmission mode 9, the UE canbe configured with one CSI-RS resource configuration. For a serving celland UE configured in transmission mode 10, the UE can be configured withone or more CSI-RS resource configuration(s). The following parametersfor which the UE shall assume non-zero transmission power for CSI-RS areconfigured via higher layer signaling for each CSI-RS resourceconfiguration:

-   -   CSI-RS resource configuration identifier (if the UE is        configured in transmission mode 10)    -   Number of CSI-RS ports.    -   CSI RS Configuration    -   CSI RS subframe configuration I_(CSI-RS).    -   UE assumption on reference PDSCH transmitted power for CSI        feedback (P_c) (if the UE is configured in transmission mode 9).    -   UE assumption on reference PDSCH transmitted power for CSI        feedback (P_c) for each CSI process, if the UE is configured in        transmission mode 10. If CSI subframe sets C_(CSI,0) and        C_(CSI,1) are configured by higher layers for a CSI process, P_c        is configured for each CSI subframe set of the CSI process.    -   Pseudo-random sequence generator parameter (n_ID)    -   CDM type parameter, if the UE is configured with higher layer        parameter CSI-Reporting-Type, and CSI-reporting-Type is set to        ‘CLASS A’ for a CSI process.    -   Higher layer parameter qcl-CRS-Info-r11 for QCL type B UE        assumption of CRS antenna ports and CSI-RS antenna ports with        the following parameters, if the UE is configured in        transmission mode 10:    -   qcl-ScramblingIdentity-r11.    -   crs-PortsCount-r11.    -   mbsfn-SubframeConfigList-r11.

P_c is the assumed ratio of PDSCH EPRE to CSI-RS EPRE (Energy PerResource Element) when UE derives CSI feedback and takes values in therange of [−8, 15] dB with 1 dB step size, where the PDSCH EPREcorresponds to the number of symbols for which the ratio of the PDSCHEPRE to the cell-specific RS EPRE.

A UE should not expect the configuration of CSI-RS and PMCH in the samesubframe of a serving cell.

For frame structure type 2 serving cell and 4 CRS ports, the UE is notexpected to receive a CSI RS Configuration index belonging to the set[20-31] for the normal CP case or the set [16-27] for the extended CPcase.

A UE may assume the CSI-RS antenna ports of a CSI-RS resourceconfiguration are quasi co-located (QCL) with respect to delay spread,Doppler spread, Doppler shift, average gain, and average delay.

A UE configured in transmission mode 10 and with QCL type B may assumethe antenna ports 0-3 associated with qcl-CRS-Info-r11 corresponding toa CSI-RS resource configuration and antenna ports 15-22 corresponding tothe CSI-RS resource configuration are quasi co-located (QCL) withrespect to Doppler shift, and Doppler spread.

If a UE is configured in transmission mode 10 with higher layerparameter CSI-Reporting-Type, CSI-Reporting-Type is set to ‘CLASS B’,and the number of CSI-RS resources configured for a CSI process is 1 ormore, and QCL type B is configured, the UE is not expected to receiveCSI-RS resource configurations for the CSI process that have differentvalues from the higher layer parameter qcl-CRS-Info-r11.

In subframes configured for CSI-RS transmission, the reference signalsequence r_(l,n) _(s) (m) shall be mapped to complex-valued modulationsymbols a_(k,l) ^((p)) used as reference symbols on antenna port p. Themapping depends on the higher layer parameter CDMType.

If CDMType does not correspond to CDM4, mapping may be done according tothe following Equation 14:

                                     [Equation  14]     a_(k, l)^((p^(′))) = w_(l^(″)) ⋅ r_(l, n_(s))(m^(′))$\mspace{79mu} {k = {k^{\prime} + {12m} + \{ {{\begin{matrix}{- 0} & {{{{for}\mspace{11mu} p^{\prime}} \in \{ {15,16} \}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 6} & {{{{for}\mspace{11mu} p^{\prime}} \in \{ {17,18} \}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 1} & {{{{for}\mspace{11mu} p^{\prime}} \in \{ {19,20} \}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 7} & {{{{for}\mspace{11mu} p^{\prime}} \in \{ {21,22} \}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 0} & {{{{for}\mspace{11mu} p^{\prime}} \in \{ {15,16} \}},{{extended}\mspace{11mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 3} & {{{{for}\mspace{11mu} p^{\prime}} \in \{ {17,18} \}},{{extended}\mspace{11mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 6} & {{{{for}\mspace{11mu} p^{\prime}} \in \{ {19,20} \}},{{extended}\mspace{11mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 9} & {{{{for}\mspace{11mu} p^{\prime}} \in \{ {21,22} \}},{{extended}\mspace{11mu} {cyclic}\mspace{14mu} {prefix}}}\end{matrix}l} = {l^{\prime} + \{ {{\begin{matrix}l^{''} & {{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{14mu} {configurations}\mspace{14mu} 0\text{-}19},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{2l^{''}} & {{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{14mu} {configurations}\mspace{14mu} 20\text{-}31},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\l^{''} & {{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{14mu} {configurations}\mspace{14mu} 0\text{-}27},{{extended}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}}\end{matrix}\mspace{79mu} w_{l^{''}}} = \{ {{{\begin{matrix}1 & {p^{\prime} \in \{ {15,17,19,21} \}} \\( {- 1} )^{l^{''}} & {p^{\prime} \in \{ {16,18,20,22} \}}\end{matrix}\mspace{79mu} l^{''}} = 0},{{1\mspace{79mu} m} = 0},1,\ldots \mspace{11mu},{{N_{RB}^{DL} - {1\mspace{79mu} m^{\prime}}} = {m + \lfloor \frac{N_{RB}^{\max,{DL}} - N_{RB}^{DL}}{2} \rfloor}}} } }} }}$

If CDMType corresponds to CDM4, mapping may be done according to thefollowing Equation 15.

                                     [Equation  15]     a_(k, l)^((p^(′))) = w_(p^(′))(i) ⋅ r_(l, n_(s))(m^(′))$k = {k^{\prime} + {12m} - \{ {{\begin{matrix}k^{''} & {{{{for}\mspace{11mu} p^{\prime}} \in \{ {15,16,19,20} \}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}},{N_{ports}^{CSI} = 8}} \\{k^{''} + 6} & {{{{for}\mspace{11mu} p^{\prime}} \in \{ {17,18,21,22} \}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}},{N_{ports}^{CSI} = 8}} \\{6k^{''}} & {{{{for}\mspace{11mu} p^{\prime}} \in \{ {16,16,17,18} \}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}},{N_{ports}^{CSI} = 4}}\end{matrix}l} = {l^{\prime} + \{ {{{\begin{matrix}l^{''} & {{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{14mu} {configurations}\mspace{14mu} 0\text{-}19},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{2l^{''}} & {{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{14mu} {configurations}\mspace{14mu} 20\text{-}31},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}}\end{matrix}\mspace{79mu} l^{''}} = 0},{{1\mspace{79mu} k^{''}} = 0},{{1\mspace{79mu} i} = {{{2k^{''}} + {l^{''}\mspace{79mu} m}} = 0}},1,\ldots \mspace{11mu},{{N_{RB}^{DL} - {1\mspace{79mu} m^{\prime}}} = {m + \lfloor \frac{N_{RB}^{\max,{DL}} - N_{RB}^{DL}}{2} \rfloor}}} }} }$

where w_(p′)(i) is determined by the following Table 6. Table 6represents the sequence w_(p′)(i) for CDM4.

TABLE 6 p′ N_(ports) ^(CSI) = 4 N_(ports) ^(CSI) = 8 [w_(p′)(0)w_(p′)(1) w_(p′)(2) w_(p′)(3)] 15 15, 17 [1 1 1 1] 16 16, 18 [1 −1 1 −1]17 19, 21 [1 1 −1 −1] 18 20, 22 [1 −1 −1 1]

OFDM Numerology

As more and more communication devices demand larger communicationcapacity, there is a need for improved mobile broadband communicationcompared to existing RAT (Radio Access Technology). Also, massive MTC(Machine Type Communications), which provides various services byconnecting many devices and objects, is one of the major issues to beconsidered in the next generation communication. In addition, acommunication system design considering a service/UE sensitive toreliability and latency in the next-generation communication is beingdiscussed. The introduction of next-generation RAT, which takes enhancedmobile broadband communication, massive MTC, and URLLC(Ultra-Reliableand Low Latency Communication) into account, is being discussed. In thepresent invention, this technology is referred to as new RAT forsimplicity.

The new RAT system uses an OFDM transmission scheme or a similartransmission scheme. Typically, it has the OFDM numerology of thefollowing Table 3.

TABLE 3 Parameter Value Subcarrier-spacing (Δf) 60 kHz OFDM symbollength 16.33 μs Cyclic Prefix(CP) length 1.30 μs/1.17 μss Systembandwidth 80 MHz (No. of available subcarriers) 1200 Subframe length0.25 ms Number of OFDM 14 symbols symbols per subframe

Self-Contained Subframe Structure

In order to minimize the latency of data transmission in the TDD systemin the new fifth-generation RAT, a self-contained subframe structure isconsidered, in which a control channel and a data channel aretime-division-multiplexed (TDM).

FIG. 14 illustrates a self-contained subframe structure to which thepresent invention is applicable.

In FIG. 14, the hatched area represents the transmission region of aphysical channel PDCCH carrying DCI, and the black area represents thetransmission region of a physical channel PUCCH for carrying UCI (UplinkControl Information).

Here, the DCI is control information that the eNB transmits to the UE.The DCI may include information on cell configuration that the UE shouldknow, DL specific information such as DL scheduling, and UL specificinformation such as UL grant. The UCI is control information that the UEtransmits to the eNB. The UCI may include a HARQ ACK/NACK report on theDL data, a CSI report on the DL channel status, and/or a schedulingrequest (SR).

In FIG. 14, the area that is not hatched or black may be used fortransmission of a physical channel PDSCH carrying downlink data, or maybe used for transmission of a physical channel PUSCH carrying uplinkdata. According to the self-contained subframe structure, DLtransmission and UL transmission may be sequentially performed in onesubframe, whereby DL data may be transmitted and UP ACK/NACK may bereceived within the subframe. As a result, the time taken to retransmitdata when a data transmission error occurs may be reduced, therebyminimizing the latency of final data transfer.

In the self-contained subframe structure, a time gap for switching froma transmission mode to a reception mode or vice versa is required forthe eNB and the UE. To this end, some OFDM symbols at the time ofswitching from DL to UL in the subframe structure are set as a guardperiod (GP). This subframe type may be referred to as a ‘self-containedSF’.

Analog Beamforming

In millimeter wave (mmW), the wavelength is shortened, and thus aplurality of antenna elements may be installed in the same area. Forexample, a total of 64 (8×8) antenna elements may be installed in a5-by-5 cm panel in a 30 GHz band with a wavelength of about 1 cm in a2-dimensional array at intervals of 0.5λ (wavelength). Therefore, inmmW, increasing the coverage or the throughput by increasing thebeamforming (BF) gain using multiple antenna elements is taken intoconsideration.

If a transceiver unit (TXRU) is provided for each antenna element toenable adjustment of transmit power and phase, independent beamformingis possible for each frequency resource. However, installing TXRU in allof the about 100 antenna elements is less feasible in terms of cost.Therefore, a method of mapping a plurality of antenna elements to oneTXRU and adjusting the direction of a beam using an analog phase shifteris considered. This analog beamforming method may only make one beamdirection in the whole band, and thus may not perform frequencyselective beamforming (BF), which is disadvantageous.

Hybrid BF with B TXRUs that are fewer than Q antenna elements as anintermediate form of digital BF and analog BF may be considered. In thecase of hybrid BF, the number of directions in which beams may betransmitted at the same time is limited to B or less, which depends onthe method of connecting B TXRUs and Q antenna elements.

Moreover, hybrid beamforming, a combination of digital beamforming andanalog beamforming, is suggested where multiple antennas are used in thenew RAT system. Here, the analog beamforming (or RF beamforming) refersto performing precoding (or combining) at the RF end. In the hybridbeamforming, the baseband end and the RF end each perform precoding (orcombining), which has the benefit of achieving performance close todigital beamforming while reducing the number of RF chains and thenumber of D(digital)/A(analog) (or A/D) converters. For convenience, thehybrid beamforming structure may be represented by N transceiver units(TXRUs) and M physical antennas. Then, digital beamforming for L datalayers to be transmitted by the transmitting end may be represented by Nby L matrices, and thereafter N converted digital signals are convertedinto analog signals through the TXRUs and then analog beamforming isapplied to represent them by M by N matrices.

FIG. 15 is a schematic diagram of a hybrid beamforming structure fromthe perspective of TXRUs and physical antennas. In FIG. 15, the numberof digital beams is L, and the number of analog beams is N.

The New RAT system is designed in such a way that the base stationchanges analog beamforming for each symbol, thereby supporting moreefficient beamforming for a UE located in a particular area.Furthermore, in FIG. 15, when N particular TXRUs and M RF antennas aredefined by a single antenna panel, the New RAT system may deploy aplurality of antenna panels to which hybrid beamforming may be appliedindividually.

When the base station uses multiple analog beams, each UE may requiredifferent analog beams for their signal reception. Thus, forsynchronization signals, system information, and paging, beam sweepingmay be taken into consideration so that the multiple analog beams to beused by the base station in a particular subframe (SF) are changed foreach symbol to allow every UE to have an opportunity to receive.

FIG. 16 is a schematic diagram of a beam sweeping operation forsynchronization signals and system information in a DL transmissionprocess.

In FIG. 16, physical resources (or physical channels) on which thesystem information in the New RAT system is transmitted by broadcastingare termed xPBCH (physical broadcast channels).

Referring to FIG. 16, analog beams that belong to different antennapanels within one symbol may be simultaneously transmitted. To measure achannel for each analog beam, as shown in FIG. 16, an approach forintroducing a beam RS (BRS), which is an RS that is transmitted using asingle analog beam (corresponding to a specific antenna panel), is beingdiscussed. The BRS may be defined for a plurality of antenna ports, andeach antenna port of the BRS may correspond to a single analog beam. Inthis case, unlike the BRS, a synchronization signal or xPBCH may betransmitted using all analog beams in an analog beam group so that acertain UE may receive it properly.

RRM Measurement in LTE

LTE systems support RRM operations for power control, scheduling, cellsearch, cell re-selection, handover, radio link or connectionmonitoring, connection establish/re-establish, etc. In this case, theserving cell may request the UE for the RRM measurement information forthe RRM operations. For example, the UE may measure cell searchinformation for each cell, reference signal received power (RSRP),reference signal received quality (RSRQ), etc., and may report themeasurement result. Specifically, in an LTE system, the UE may receive“measConfig” as a higher-layer signal for RRM measurement from theserving cell. In this case, the UE may measure RSRP or RSRQ according tothe “measConfig” information. In this case, RSRP, RSRQ, and RSSIaccording to the TS 36.214 document for LTE systems can be defined asfollows:

[RSRP]

Reference signal received power (RSRP) is defined as the linear averageover the power contributions (in [W]) of the resource elements thatcarry cell-specific RSs (CRs) within the considered measurementfrequency bandwidth. For RSRP determination, CRS RO shall be usedaccording to TS 36.211 [3]. If the UE can reliably detect that R1 isavailable, it may use R1 in addition to R0 to determine RSRP.

The reference point for the RSRP shall be the antenna connector of theUE.

If receiver diversity is in use by the UE, the reported value shall notbe lower than the corresponding RSRP of any of the individual diversitybranches.

[RSRQ]

Reference Signal Received Quality (RSRQ) is defined as the ratioN×RSRP/(E-UTRA carrier RSSI), where N is the number of RBs of the E-UTRAcarrier RSSI measurement bandwidth. The measurements in the numeratorand denominator shall be made over the same set of resource blocks.

E-UTRA Carrier Received Signal Strength Indicator (RSSI) comprises thelinear average of the total received power (in [W]) observed/measured bythe UE, only in OFDM symbols containing reference symbols for antennaport 0, in the measurement bandwidth, over N number of resource blocksfrom all sources (including co-channel serving and non-serving cells),channel interference, thermal noise etc. If higher-layer signalingindicates certain subframes for performing RSRQ measurements, then RSSIis measured over all OFDM symbols in the indicated subframes.

The reference point for the RSRQ shall be the antenna connector of theUE.

If receiver diversity is in use by the UE, the reported value shall notbe lower than the corresponding RSRQ of any of the individual diversitybranches.

[RSSI]

The received wide band power, including thermal noise and noisegenerated in the receiver, within the bandwidth defined by the receiverpulse shaping filter.

The reference point for the measurement shall be the antenna connectorof the UE.

If receiver diversity is in use by the UE, the reported value shall notbe lower than the corresponding UTRA carrier RSSI of any of theindividual receive antenna branches.

In accordance with the above-mentioned definitions, the UE configured tooperate in the LTE system may measure the RSRP through IE (informationelement)—associated with Allowed Measurement Bandwidth (AMB) transmittedin SIB3 (System Information Block Type 3) in the case of Intra-Frequencymeasurement, or may measure the RSRP at one bandwidth selected fromamong 6RB (Resource Block), 15RB, 25RB, 50RB, 75RB, and 100RB throughallowed measurement bandwidth (AMB) transmitted in SIBS (SystemInformation Block Type 5) in the case of Inter-frequency measurement.Alternatively, if the information element (IE) is not present, the UEconfigured to operate in the LTE system may measure the RSRP in afrequency bandwidth of the entire DL system as a default. In this case,if the UE receives the allowed measurement bandwidth, the UE may assumethat the corresponding value is a maximum measurement bandwidth, suchthat the UE can freely measure the RSRP value within the correspondingvalue. However, if the serving cell transmits the IE defined asWB(wideband)-RSRQ and sets the allowed measurement bandwidth to SORB orhigher, the UE must calculate the RSRP value regarding the entireallowed measurement bandwidth. Meanwhile, RSSI may be measured in thefrequency bandwidth allocated to the receiver of the UE according to theRSSI bandwidth definition.

FIG. 17 illustrates a panel antenna array to which the present inventionis applicable.

Referring to FIG. 17, the panel antenna array consists of Mg panels inthe horizontal domain and Ng panels in the vertical domain, and eachpanel may consist of M columns and N rows. Particularly, the panels asused herein are illustrated with respect to X-pol (cross polarization)antennas. Accordingly, the total number of antenna elements in FIG. 17may be 2*M*N*Mg*Ng.

Port Layout

Codebooks may be defined as various types. In NR (New RAT), there aremainly two types of codebooks: Type 1 codebook and Type2 codebook.Further, each type may be sub-divided depending on whether it is acodebook for a single panel or a codebook for multi-panels (e.g., Type 1single/multi-panel codebook and Type 2 single/multi-panel codebook).

For Type 1 single panel codebook, W1 may be defined by the followingEquation 16. Here, W1 denotes a first PMI having long-term, wideband,and beam selection characteristics.

$\begin{matrix}{{W_{1} = \begin{bmatrix}B_{1} & 0 \\0 & B_{2}\end{bmatrix}},{B_{i} = {\lbrack {b_{0}^{i},\ldots \mspace{14mu},b_{L - 1}^{i}} \rbrack.}}} & \lbrack {{Equation}\mspace{14mu} 16} \rbrack\end{matrix}$

At least for rank 1 and rank 2, the number (L) of candidate DFT(Discrete Fourier Transform) beams in B (or Bi) in W1 may be 1, 2, 4and/or 7. The L value may be configured by the network (e.g., basestation).

For L>1, L beams may be selected freely by the UE. Alternatively, atleast one beam group pattern may be defined, and an example of such abeam group pattern will be described below with reference to FIGS. 18and 19. The beam group pattern may be configured by the network (e.g.,base station). A beam pattern may be reported by the UE. Alternatively,L beams may be selected freely by gNB.

Selection of L beams may apply to rank 1 and rank 2 alike ordifferently. For L=1, W1 may be defined by the following Equation 17:

$\begin{matrix}{W_{1} = \begin{bmatrix}v & 0 \\0 & v\end{bmatrix}} & \lbrack {{Equation}\mspace{14mu} 17} \rbrack\end{matrix}$

FIG. 18 illustrates candidate beam group patterns for L=2 in a 2D portlayout applicable to the present invention. In this drawing, patternedsquares represent L selected beams.

FIG. 19 illustrates candidate beam group patterns for L=4 in a 2D portlayout applicable to the present invention. In this drawing, patternedsquares represent L selected beams.

In a 1D port layout, a beam group pattern includes a row of beams forL>1 that are uniformly and/or non-uniformly separated by d. For L>1, asingle value or multiple values may be supported for d1 and d2.

Proposal of Codebooks in NR

In wireless communication systems using panel array antennas, includingNew RAT, narrow beams are formed as beamforming using massive antennasis performed, and the implementation of a panel antenna array mayeliminate linear increments between antenna ports. Thus, the performanceof a DFT-based codebook, used in LTE, LTE-A, etc., may be degraded.Accordingly, the present invention proposes a codebook structuresuitable for a panel array antenna.

Firstly, a 2D DFT beam to be applied to a 2D antenna array within onepanel may be defined by Equation 18:

$\begin{matrix}{{{W_{m_{1},m_{2}} = \frac{v_{m_{1}} \otimes u_{m_{2}}}{\sqrt{N_{1}N_{2}}}}v_{m_{1}} = \lbrack {1\mspace{11mu} {\exp ( {j\frac{2\; \pi \; m_{1}}{o_{1}N_{1}}} )}L\mspace{14mu} \exp \; ( {j\frac{2\; \pi \; {m_{1}( {N_{1} - 1} )}}{o_{1}N_{1}}} )} \rbrack^{T}}{u_{m_{2}} = \lbrack {1\mspace{11mu} {\exp ( {j\frac{2\; \pi \; m_{2}}{o_{2}N_{2}}} )}L\mspace{14mu} \exp \; ( {j\frac{2\; \pi \; {m_{2}( {N_{2} - 1} )}}{o_{2}N_{2}}} )} \rbrack^{T}}} & \lbrack {{Equation}\mspace{14mu} 18} \rbrack\end{matrix}$

where m1 and m2 represent the indices of a 1D-DFT codebooks in first anddomains, respectively, N1 and N2 represent the numbers of antenna portsper pol in first and second dimensions in a panel, and o1 and o2represent the oversampling factors in first and second dimensions in apanel.

In FIG. 17, M and N represent antenna elements (hereinafter, M isreferred to as a first domain (horizontal) parameter, and N is referredto as a second domain (vertical) parameter, for convenience ofexplanation). According to the results of performing antennavirtualization on a plurality of antenna elements according to aspecific vector and then performing antenna element-to-port mapping, thenumber of ports in the first and second domains is defined by N1 and N2,respectively. When N1′ and N2′ are defined as the number of ports perpanel, the total number (Ntot) of antenna ports to be considered in thepresent invention is defined as P*Mg*Ng*N1′*N2′, and P may be set to 2in the case of an X-pol antenna and 1 in the case of a co-pol antenna.

FIG. 20 is a view illustrating a non-uniform array according to anexemplary embodiment of the present invention.

Referring to FIG. 20, vertical virtualization on a panel array with 32elements (i.e., M=4, N=2, P=2) for each panel results in P=2, N1′=4,N2′=1, Mg=2, Ng=2, which is a total of 32 ports. While antenna ports maycorrespond to antenna elements by antenna virtualization, the antennaports in the present invention, after the virtualization of a singleantenna element or multiple antenna elements, are generally referred toas an “antenna port” for convenience of explanation. Antenna portinformation for beamforming (e.g., {N1, N2, O1 and O2}, and/or {Mg, Ng,N1′, N2′, O1 and/or O2}) may be signaled by higher-layer signaling oragreed in advance between the UE and the network.

The Ntot value may vary, but should conform to a codebook structure thatis integrally applicable to antenna ports supported in LTE systems, suchas 2, 4, 8, 12, 16, 20, 24, 28, and 32-ports. To this end, the presentinvention considers a multi-stage codebook structure, and an example oftriple stages is as shown in the following Equation 19:

W=W1*W2*W3  [Equation 19]

where a particular codebook matrix may be replaced with W1 (first PMI)or W2 (second PMI) in a dual-stage codebook structure used in LTE andLTE-A.

A 3GPP Rel-13 codebook follows dual structures of Rel-10 and Rel12codebooks. That is, a final codebook is formed by multiplying W1 and W2,with W1 having the long-term, wideband, and beam group selectioncharacteristics and W2 having the short-term, subband, and beamselection and co-phasing characteristics.

The difference with the Rel-10 and Rel-12 codebooks is that, since anantenna port layout to be considered includes two dimensions, the beamsin the codebooks are described as a Kronecker product of a vertical beamand a horizontal beam. A 3GPP Rel-13 1-2 codebook may be expressed bythe following Equation 20:

$\begin{matrix}{\mspace{79mu} {{{W = {W_{1}W_{2}}}\mspace{20mu} {{W_{m_{1},m_{2},n}^{(1)} = {\frac{1}{\sqrt{2\; N_{1}N_{2}}}\begin{bmatrix}{v_{m_{1}} \otimes u_{m_{2}}} \\{\phi_{n}{v_{m_{1}} \otimes u_{m_{2}}}}\end{bmatrix}}},\mspace{20mu} {\phi_{n} = {\exp ( \frac{j\; 2{\pi n}}{4} )}},{n = 0},1,2,3,{W_{m_{1},m_{2},n}^{(2)} = {\frac{1}{\sqrt{2\; N_{1}N_{2}}}\begin{bmatrix}{v_{m_{1}} \otimes u_{m_{2}}} & {v_{m_{1}} \otimes u_{m_{2}}} \\{\phi_{n}{v_{m_{1}} \otimes u_{m_{2}}}} & {{- \phi_{n}}{v_{m_{1}} \otimes u_{m_{2}}}}\end{bmatrix}}},\mspace{20mu} {\phi_{n} = {\exp ( \frac{j\; 2{\pi n}}{4} )}},{n = 0},1}}\mspace{20mu} {v_{m_{1}} = \lbrack {1\mspace{11mu} {\exp ( {j\frac{2\; \pi \; m_{1}}{o_{1}N_{1}}} )}L\mspace{14mu} \exp \; ( {j\frac{2\; \pi \; {m_{1}( {N_{1} - 1} )}}{o_{1}N_{1}}} )} \rbrack^{T}}\mspace{20mu} {u_{m_{2}} = \lbrack {1\mspace{11mu} {\exp ( {j\frac{2\; \pi \; m_{2}}{o_{2}N_{2}}} )}L\mspace{14mu} \exp \; ( {j\frac{2\; \pi \; {m_{2}( {N_{2} - 1} )}}{o_{2}N_{2}}} )} \rbrack^{T}}}} & \lbrack {{Equation}\mspace{14mu} 20} \rbrack\end{matrix}$

where W{circumflex over ( )}(1) represents the final form of the rank 1codebook, and W{circumflex over ( )}(2) represents the final form of therank 2 codebook.

Here, N1 and N2 are the number of antenna ports per polarization in 1stand 2nd dimensions, and o1 and o2 are the oversampling factors in firstand second dimensions.

m1 and m2 represent methods of selecting a DFT vector in horizontal andvertical (or first and second) domains. A particular W1 (i.e., firstPMI) 2D beam group (i.e., Codebook Configs 1 to 4) may be createdthrough ml (for rank 2, m1 and m1′) and m2 (for rank 2, m2 and m2′). Thesubscript n represents co-phasing.

That is, the 3GPP Rel-13 codebook can be viewed as a two-dimensionalextension of 8Tx(8 port transfer) codebook of Rel-10 using a Kroneckerkproduct.

Proposal 1) Analog Codebook

This proposal proposes a method for reporting CSI information for analogbeamforming using a codebook.

In an embodiment, one (e.g., W1) of the multi-stages of Equation 19performs the function/role of codeword selection corresponding to Tx/Rxanalog beamforming, or an analog codebook may be generated by a singlecodebook matrix.

In analog beamforming, an analog codebook may be configured by aweighting vector for TXRU virtualization. Using a 2D sub-array model inFD-MIMO, it may be configured by the following Equation 21:

$\begin{matrix}{{{v_{l,i} = {\frac{1}{\sqrt{L}}{\exp ( {{- j}\frac{2\; \pi}{\lambda}( {l - 1} )d_{H}\sin \mspace{11mu} \vartheta_{i}} )}\mspace{14mu} {for}}}\text{}{{l = 1},\ldots \mspace{14mu},L,{o = 1},\ldots \mspace{14mu},{o_{1\; {TXRU}}L}}w_{k,o} = {\frac{1}{\sqrt{K}}{\exp ( {{- j}\frac{2\; \pi}{\lambda}( {k - 1} )d_{V}\cos \mspace{11mu} \theta_{{etilt},o}} )}\mspace{14mu} {for}}}{{k = 1},\ldots \mspace{14mu},K,{o = 1},\ldots \mspace{14mu},{o_{2\; {TXRU}}K}}} & \lbrack {{Equation}\mspace{14mu} 21} \rbrack\end{matrix}$

where dv and dH are the spacing between each antenna element, λ is thecarrier frequency, K is the number of antenna elements in the N1 domainper TXRU, L is the number of antenna elements in the N2 domain per TXRU,O_1TXRU and O_2TXRU are the oversampling factors of 1-DFT beams formedby the elements in each domain of TXRU, the length of wo is given byK=M/N1′, and the length of vi is given by L=N/N2′. ϑ_(i),θ_(etilt,o),are specific directivity angles in N1 and N2 domains, respectively, andmay be expressed by scan and tilt angles if N1 is a horizontal domainand N2 is a vertical domain.

Accordingly, the final form of a Tx analog beam may be determined as inEquation 22:

w _(k) ⊗v _(l)  [Equation 22]

Equation 22 corresponds to when antenna element indexing forvirtualization is performed first in the N2 direction. If antennaelement indexing for virtualization is performed first in the N2direction, Equation 22 may be transformed into the following Equation23:

v ₁ ⊗w _(k)  [Equation 23]

An analog beam may be directed in 2D as described above, or may bedirected only in 1D direction by using a vector for horizontal orvertical virtualization alone. In the present invention, exemplaryembodiments will be described with respect to, but not limited to, 2Danalog beams based on Equation 22 for convenience of explanation.

Each vector in Equation 21 may be expressed in the same manner by DFTbeams in Equation 18 by a mathematical relationship. For example,Equation 21 may be transformed into the following Equation 24 byexpressing each vector by tilting.

$\begin{matrix}{\theta_{tilt} = {\cos^{- 1}( \frac{{- m_{1}}\lambda}{o_{2\;,{TXRU}}K\; d_{v}} )}} & \lbrack {{Equation}\mspace{14mu} 24} \rbrack\end{matrix}$

Using Equation 24, Equation 21 may be expressed by the followingEquation 25:

$\begin{matrix}{\mspace{79mu} {{v_{l} = {\frac{1}{\sqrt{L}}\lbrack {1\mspace{11mu} {\exp ( {j\frac{2\; \pi \; l}{o_{1\;,{TXRU}}L}} )}L\mspace{11mu} {\exp ( {j\frac{2\; \pi \; {l( {L - 1} )}}{o_{1\;,{TXRU}}L}} )}} \rbrack}^{T}}{w_{k} = {\frac{1}{\sqrt{K}}\lbrack {1\mspace{11mu} {\exp ( {j\frac{2\; \pi \; k}{o_{2\;,{TXRU}}K}} )}L\mspace{11mu} {\exp ( {j\frac{2\; \pi \; {k( {K - 1} )}}{o_{2\;,{TXRU}}K}} )}} \rbrack}^{T}}}} & \lbrack {{Equation}\mspace{14mu} 25} \rbrack\end{matrix}$

where k=0, . . . ,o_(K−1), l=0, . . . ,o_(L−1). Then, the maximum sizeof an analog codebook may be represented by multiplying L*O_1TXRU andK*O_2TXRU. In the analog codebook, the resulting tilting angle and thescan angle may be configured by uniformly configuring all azimuth anglesand zenith angles (e.g., Equation 26, and the above example assume thatthe zenith angle ranges from −pi to pi and the azimuth angle ranges from−pi/3 to pi/3), and by uniformly dividing the boundary of analog beamsby the number of analog beams as in θ₁≤θ_(tilt)θ₂ and ϑ≤ϑ_(scan)≤ϑ₂. Inthis case, the base station may inform the UE of the number of analogbeams used and/or the boundary value of the angle of analog beams byRRC.

$\begin{matrix}{{\vartheta_{{scan},1} = {{- \frac{\pi}{3}} + {\frac{2\; \pi}{3o_{1\;,{TXRU}}L}{l( {{l = 1},{\ldots \mspace{20mu} o_{1,{TXRU}}L}} )}}}},{\theta_{{tilt},k} = {\frac{\pi}{o_{2\;,{TXRU}}K}{k( {{k = 1},{\ldots \mspace{20mu} o_{2\;,{TXRU}}K}} )}}}} & \lbrack {{Equation}\mspace{14mu} 26} \rbrack\end{matrix}$

The above-explained analog codebook for antenna virtualization may bedivided into two types of codebooks:

Selection Codebook

NP (Non-Precoded) CSI-RS based Analog codebook

Hereinafter, the selection codebook and the NP CSI-RS based analogcodebook will be proposed.

In an analog beam selection codebook, particular N_A analog beamformingbeams (e.g., the N_A value may be set to L*O_1TXRU*K*O_2TXRU orset/defined to a specific value the base station informs the UE of) maybe mapped to N_A CSI-RS ports (or specific ports for analogbeamforming), and the UE may report a (selected) PMI using a portselection codebook.

The UE may report a number of beams pre-agreed with the base station (orindicated by the base station), including the best beam, the first andsecond best beams, or the best and worst beams. To this end, the basestation may indicate information such as K, O_1TXRU, L, O_2TXRU, etc. orthe N_A value to the UE through higher-layer signaling or may pre-agreewith the UE about this. The tilting angle or scan angle mainly used forthe UE may be limited depending on the UE's channel environment. Thus,to reduce the overhead of analog beam sweeping, the base station mayinform the UE of the number of analog beams used for beam sweepingand/or the number of analog beams to be reported by higher-layersignaling or pre-agree with the UE about this.

When the selection codebook is used, a single analog beam is mapped to asingle antenna port and transmitted, and the UE configures a selectionvector by the codebook and report it to the base station. That is, inthis case, the codebook is configured by an analog beam selectionvector, and the codeword is as shown in Equation 27, and the UE reportsthe i index of Equation 27 to the base station.

$\begin{matrix}{{e_{i} = \lbrack {{\underset{\underset{i}{}}{0,{\ldots \mspace{14mu} 1},}\mspace{11mu} \ldots}\mspace{14mu},0} \rbrack^{T}},{{{where}\mspace{14mu} i} = 1},\ldots \mspace{14mu},N_{A}} & \lbrack {{Equation}\mspace{14mu} 27} \rbrack\end{matrix}$

Using Equation 27, the best Tx analog beam reporting codebook may beexpressed as in Equation 28:

W _(analog,Tx,i)=[e _(i)]∈C ^(N) ^(A) ^(×1)  [Equation 28]

In this case, the number of feedback bits in the codebook is ┌log₂N_(A)┐. For example, for N_A=32, a total of 5 bits of a feedback payloadis required.

When the UE additionally reports the best beam or the worst beam, the UEmay be newly defined and used as an indicator indicating the number ofbeams to be reported, or an RI in an LTE system may be newly defined andused as an indicator indicating the number of beams. For example, whenthe first beam is selected as the best beam and the fourth beam isselected as the worst beam, the UE may report, to the base station, RI=2and a PMI index corresponding to W² _(analog,Tx)=[e₁,e₄]∈C^(N) ^(A)^(×2), obtained by applying the first beam and the fourth beam toEquation 28. And/or, the UE may assume a rank 1 restriction on each beamand report a PMI with a different period and/or offset. In this case,the number of feedback bits to be reported is ┌log₂(N_(A)(N_(A)−1)┐.And/or, the UE may use the codebook for the purpose of indicating therange of a TX analog beam (e.g., for the purpose of indicating θ₁ and θ₂in θ₁≤θ_(tilt)≤θ₂).

While this embodiment has been exemplified with respect to verticaltilting/domain, the present invention is not limited thereto and thiscodebook may be used for the purpose of indicating horizontaltilting/domain or 2-D tilting/domains where both horizontal and verticaltilting/domains are used. Moreover, in this embodiment, the UE may beunderstood/interpreted as providing the base station with information onan analog codebook subset restriction, and this may be applicable todigital codebooks.

In analog beam sweeping, the payload size may not be a big problembecause of the long term and wideband characteristics. Thus, when theanalog beam selection codebook is used, analog beams may be fed back ina linear combination as shown in Equation 29 may be considered for moreprecise feedback.

$\begin{matrix}{\frac{1}{{\sum\limits_{i \in S_{l}}\; {c_{i}e_{i}}}}{\sum\limits_{i \in S_{l}}\; {c_{i}e_{i}}}} & \lbrack {{Equation}\mspace{14mu} 29} \rbrack\end{matrix}$

where S_(l) is a set of l-th beams participating in beam combining, andci is a combination coefficient which may have a particular complexvalue and be configured by c_(i,j,k)=α_(i,j)exp(jϕ_(i,k)). At least someof the elements of S_(l), a_(i,j),ϕ_(i,k) may be pre-agreed between thebase station and the UE, and the base station may indicate them to theUE by RRC. For example, if the total number of analog beams used for Txbeam sweeping is 4 and the number of beams participating in combining is2, S_(l)∈{(1,2),(1,3),(1,4),(2,3),(2,4),(3,4)}, a_(i,j)={1,0.5,0.25,0},ϕ_(i,k)={1,j,−1, −j} may be established. In the above example, thenumber of required feedback bits is 3+2+2=7, and at least some of thefeedback elements/content may be joint-encoded and fed back/reported.And/or, each element/content may be fed back with a different periodand/or different feedback granularity/unit (e.g.,Wideband(WB)/Subband(SB)). A combining codebook, in comparison with acodebook only using a selection through Equation 27, has the advantageof being capable of implementing an analog codebook with a relativelyhigher granularity.

If the UE is located in an environment with a lot of interference (e.g.,at a cell boundary), performance degradation may get severe due tointerference from an analog beam transmitted from an interfering TRP(Transmission Reception Point). In this case, the UE may measure theinterference by the codebook and report to the base station information(e.g., {0.5,0.25,0.125,0}*P, where P is transmitted power) on thereduced power level due to the interference, along with/simultaneouslywith the corresponding codeword.

The foregoing embodiment has been described with respect to a Tx beamsweeping operation of the base station. However, if the UE performs Rxbeam sweeping, the UE may report information about this to the basestation to let the base station know the UE's UL beamforminginformation. That is, similarly to Equation 25, an Rx analog beam may berepresented by Equation 30:

$\begin{matrix}{{{r_{a} = {\frac{1}{\sqrt{A}}\lbrack {1\mspace{11mu} {\exp ( {j\frac{2\; \pi \; a}{o_{{1r},{TXRU}}A}} )}L\mspace{11mu} {\exp ( {j\frac{2\; \pi \; {a( {A - 1} )}}{o_{{1r},{TXRU}}A}} )}} \rbrack}^{T}},\mspace{20mu} {a = 0},\ldots \mspace{14mu},{{o_{{1r},\; {TXRU}}A} - 1}}{{s_{b} = {\frac{1}{\sqrt{B}}\lbrack {1\mspace{11mu} {\exp ( {j\frac{2\; \pi \; b}{o_{{2\; r}\;,{TXRU}}B}} )}L\mspace{11mu} {\exp ( {j\frac{2\; \pi \; {b( {B - 1} )}}{o_{{2r}\;,{TXRU}}B}} )}} \rbrack}^{T}},\mspace{20mu} {b = 0},L,{{o_{{2\; r}\;,{TXRU}}B} - 1}}} & \lbrack {{Equation}\mspace{14mu} 30} \rbrack\end{matrix}$

where A and B represent the numbers of antenna elements in first andsecond domains of the UE's TXRU, and O_(1r,TXRU) and O_(2r,TXRU)represent the oversampling factors in first and second domains of ananalog DFT codebook.

The final 2D(or 1D) DFT beam may be expressed as a Kronecker productr_(a)⊗s_(b) or s_(b)⊗r_(a) using Equation 30, as in Equation 22.

For configuring a UL codebook, the UE may additionally give feedback tothe base station about information of A, B, O_(1r,TXRU), and O_(2r,TXRU)or the number of Rx beamforming. And/or, the UE may additionally givefeedback to the base station about the port index direction (that is,r_(a)⊗s_(b) or s_(b)⊗r_(a)) or pre-agree with the base station about it.The entire size (Nrx,tot) of the Rx analog beamforming codebook may be‘A*B*O_(1r,TXRU)*O_(2r,TXRU)’, and the UE's Rx beamforming selectioncodebook may be represented by Equation 31:

W _(analog,Rx,j)=[e _(j)]∈C ^(N) ^(A,RX) ^(×1)  [Equation 31]

where N_(A,RX) represents the number of Rx beamforming.

Among all the analog codebooks of W_(analog,Tx)⊗W_(analog,Rx), Tx-Rxbeam pair codebooks, for example, may be reported collectively orindependently, and may have different feedback periods, offsets, and/orfeedback granularities/units (e.g., wideband/suband/partial-band).Alternatively, RI may be used in order for the UE to indicate Rxbeamforming. For example, if RI=2 is reported, the base station mayrecognize that Rx beamforming is reported (along with Tx beamforming),and may calculate each Tx-Rx beamforming by the codebooks ofW_(analog,Tx)⊗W_(analog,Rx).

In the above-described analog beamforming selection codebook, complexityincreases linearly according to the number of analog beamformed ports.That is, for N_A=128, the number of CSI-RS ports required for oneresource is 128, and it may be inefficient to transmit all these manyports in each PRB pair. Accordingly, CSI-Rs Comb-type transmission maybe taken into consideration, in which all analog beamformed CSI-RS portsare divided into N sub-port groups and the N sub-port groups are mappedone-to-one to N PRB pairs so that the N sub-port groups are transmittedto every N PRB pairs (i.e., CSI-RS ports required for one resource aredivided and transmitted across N PRB pairs). For example, for N_A=128and N=4, ports corresponding to 0th to 31th beams may be transmitted in0, 4, 8, . . . PRB-pairs (i.e., 4n PRB-pairs (n=0,1,2 . . . )), portscorresponding to 32th to 63th beams may be transmitted in 1, 5, 9, . . .PRB-pairs (i.e., 4n+1 PRB-pairs(n=0,1,2 . . . )), ports corresponding to64th to 95th beams may be transmitted in 2, 6, 10, PRB-pairs(i.e., 4n+2PRB-pairs(n=0,1,2 . . . )), and ports corresponding to 96th 127th beamsmay be transmitted in 3, 7, 11, . . . PRB-pairs(i.e., 4n+3PRB-pairs(n=0,1,2 . . . )). Alternatively, ports (32 ports in the aboveexample) corresponding/included in each sub-port group may betransmitted with different time offsets and/or periods for each sub-portgroup (and/or for each port in each sub-port group).

To reduce overhead in terms of the UE's reporting, port selection may beperformed by using RI for the purpose of indicating the above-mentionedtime offset and/or frequency offset. For example, if the best analogbeam is the 64th beam in the above example, the UE may report RI-3 andPMI=1(W_(analog,Tx,1)=[e₁]∈C^(32×1)) to the base station.

The above-described selection-based codebook may be used solely for thepurpose of beam management, and may have a higher priority level thanother CSIs (e.g., i1(first PMI), i2(second PMI), RI, CQI and/or CRI).Also, if the beam gain is lower than or equal to a particular threshold,the UE may trigger CSI-RS port transmission for the selection codebookor report a beam index (e.g., the second best beam index) different fromthe beam index reported immediately before reference resource reception.

Hereinafter, an NP CSI-RS based analog codebook will be described.

In beam sweeping, as the number of beams increases (i.e., as K, L, o1,and o2 increase), a larger number of OFDM symbols used for beam sweepingand/or more CSI-RS ports are required and the complexity of calculationby the UE increases much. If the total number of antenna elements or K*Lis equal to the number of CSI-RSs supported in NR, the UE may measurechannels and report the best analog beam and/or digital beam by using NPCSI-RS (i.e., through 1:1 element-to-port mapping).

In an example, Equation 32 may be configured as a final codebook byusing Equation 19. In this case, when the UE reports an analog codebook,the analog codebook may be reported based on a multi-stage codebook(e.g., triple-stages as in Equation 32), and the analog codebook may beused as one component of the multi-stage codebook.

$\begin{matrix}\begin{matrix}{W = {W_{a}W_{1}W_{2}}} \\{= {\underset{\underset{{Analog}\mspace{11mu} {codebook}}{}}{\begin{bmatrix}w_{a\; 1} & 0 & 0 \\0 & \ddots & 0 \\0 & 0 & w_{a,{ports}}\end{bmatrix}}\mspace{11mu} \underset{\underset{{Digital}\mspace{11mu} {dual}\mspace{11mu} {stage}\mspace{11mu} {codebook}}{}}{W_{1}W_{2}}}}\end{matrix} & \lbrack {{Equation}\mspace{14mu} 32} \rbrack\end{matrix}$

Analog codebooks (w_(ai)∈C^(N) ^(A) ^(×1)(i=1, . . . ,N_(ports), whereN_(ports) is the number of digital ports)) positioned in the diagonalterm of the first matrix of Equation 32 may be configured by Equation 22or 23, and W1 and W2 may be an LTE codebook or a digital codebook to bedescribed later. Moreover, for w_(a1)=L=w_(a1N) _(ports) , the sameanalog beam is applied to all digital ports, in which case the UE mayonly give feedback/report of the PMI of a representative analog beam forall the ports. However, it should be noted that, for more precise CSIfeedback, the UE may perform feedback/report assuming w_(a1)≠L≠w_(a1N)_(port) using different analog beams for every port. In this case, theremay be a disadvantage that the number of feedback bits increases byN_ports, as compared to using the same analog beam for every port.However, PMI (i.e., Wa) feedback on analog beams has a very long termcharacteristic (e.g., an integer multiple of digital W1 or RI), and theoverhead increase may not be that large from the entire systemperspective.

Accordingly, for efficient use of the codebook, the base station maytransmit NP CSI-RS in K*L ports in the first CSI-RS resource accordingto the UE's analog codebook feedback period, assuming that the sameanalog beam applies to every port. In this case, the UE may report thebest analog beam index to the base station, and, with this, the basestation may transmit, to the UE, N_ports CSI-RS using analog beamforming(corresponding to the analog beam index reported by the UE) for thesecond CSI-RS resource. The UE may give report/feedback (i.e., digitalcodebook feedback) to the base station about the RI, PMI and/or CQIfor/corresponding to N_ports. The aforementioned two resources (i.e.,the first and second CSI-RS resources) may have different periods and/oroffsets. If collision occurs between the two resources, the resource foranalog beamforming (i.e., the resource for determining an analog beam;the first CSI-RS resource in the above example) has a higher prioritylevel.

Alternatively, to apply a codebook with high granularity, the basestation may transmit CSI-RS using K*L*N_ports NP CSI-RS ports in oneresource, and the UE may report the best PMI, CQI and/or RI to the basestation based on the CSI-RS.

Proposal 2) Digital Codebook

In the New RAT, LTE codebooks or class A codebook may be re-used. Suchcodebooks have a dual-stage structure, and examples of this structureinclude Rel-10 8Tx, Rel-12 4Tx, Rel-13 12Tx, 16Tx, Rel-14 20-, 24-, 28-,and 32Tx codebooks. In the dual-stage structure (i.e., W=W1*W2), W1serves to determine a specific number of beam groups with thelong-term/wideband characteristics, and W2 serves to select beams withina beam group with the short-term/subband characteristics, determined asW1, and perform co-phasing under an X-pol antenna situation.

Preferably, codebooks used in the New RAT are configured within oneframework, and it is expected that configuring a codebook withconfiguration information such as parameters N1 and N2 for configuring aTX port and o1 and o2 for configuring a codebook will make it easy tomaintain scalability and implement the UE.

In an LTE 2-port codebook, rank 1 is configured by QPSK (quadraturephase-shift keying) (indices 0,1,2, and 3 of Table 4), and rank 2 isconfigured by QPSK (indices 0, 1, and 2 of Table 4). However, if analogbeams are applied to ports to make the beams sharper, it may be betterto increase beam granularity in terms of performance.

Accordingly, the present invention proposes to configure a 2-portcodebook of rank 1 and rank 2 using 8-PSK for co-phasing, as in Table 4,in order to increase 2-port granularity.

TABLE 4 Codebook Number of layers v index 1 2 0 .$\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\1\end{bmatrix}$ ${\frac{1}{\sqrt{2}}\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}}\quad$ 1 $\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\{- 1}\end{bmatrix}$ ${\frac{1}{2}\begin{bmatrix}1 & 1 \\1 & {- 1}\end{bmatrix}}\quad$ 2 $\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\j\end{bmatrix}$ ${\frac{1}{2}\begin{bmatrix}1 & 1 \\j & {- j}\end{bmatrix}}\quad$ 3 $\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\{- j}\end{bmatrix}$ $\frac{1}{2\sqrt{2}}\begin{bmatrix}\sqrt{2} & \sqrt{2} \\{1 + j} & {{- 1} - j}\end{bmatrix}$ 4 $\frac{1}{2}\begin{bmatrix}\sqrt{2} \\{1 + j}\end{bmatrix}$ $\frac{1}{2\sqrt{2}}\begin{bmatrix}\sqrt{2} & \sqrt{2} \\{1 - j} & {{- 1} + j}\end{bmatrix}$ 5 $\frac{1}{2}\begin{bmatrix}\sqrt{2} \\{1 - j}\end{bmatrix}$ — 6 $\frac{1}{2}\begin{bmatrix}\sqrt{2} \\{{- 1} + j}\end{bmatrix}$ — 7 $\frac{1}{2}\begin{bmatrix}\sqrt{2} \\{{- 1} - j}\end{bmatrix}$ —

And/or, the base station may configure a codebook bit field for the UEto set whether the final codebook is QPSK or 8-PSK. For example, if theUE is given a 2-bit field from the base station, the UE may use thecodebooks of the indices 0 to 3 in Table 4, and if the UE is given a3-bit field from the base station, the UE may use the codebooks of theindices 0 to 7 in Table 4. This may be used for a purpose similar to acodebook subset restriction. While the existing codebook subsetrestriction cannot reduce feedback bits, the above proposed method mayreduce feedback bits to thereby reduce uplink overhead.

In another embodiment, if different analog beamforming is performed foreach port and there are many antenna elements for virtualization thatconstitute a single analog beam to form very sharp beams, the codebookperformance improvement caused by digital codebook application isexpected to be not very high. In this case, it may be more efficient toapply different beams to two ports and select only a particular port. Inthis case, a 2-port codebook configuration may be proposed as in Table5.

TABLE 5 Codebook Number of layers index 1 2 0 $\quad\begin{bmatrix}1 \\0\end{bmatrix}$ ${\frac{1}{\sqrt{2}}\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}}\quad$ 1 $\quad\begin{bmatrix}0 \\1\end{bmatrix}$

In the proposal according to Table 5, no PMI feedback (i.e., beamselection) is required for rank 2.

In another embodiment, a codebook having codewords with differentmagnitudes for different ports may be configured, and an example of thisis as shown in Equation 33:

$\begin{matrix}{{{\frac{1}{\sqrt{1 + \alpha^{2}}}\begin{bmatrix}1 \\{\alpha \; \varphi_{n}}\end{bmatrix}}\mspace{14mu} {for}\mspace{14mu} {Rank}\mspace{14mu} 1}{{\frac{1}{\sqrt{2 + {2\alpha^{2}}}}\begin{bmatrix}1 & \alpha \\{\alpha \; \varphi_{n}} & {- \varphi_{n}}\end{bmatrix}}\mspace{14mu} {for}\mspace{14mu} {Rank}\mspace{14mu} 2}} & \lbrack {{Equation}\mspace{14mu} 33} \rbrack\end{matrix}$

As exemplified in Equation 33, in a 2-port codebook, a port may have aparticular magnitude that is equal to or smaller than that of anotherport. For example, in Equation 33, α={1,0.5,0.25,0}. If α is 1, thecodebook has the characteristics of the codebook exemplified in Table 4,and if α is 0, the codebook is similar to the port selection codebookexemplified in Table 5. α may be applied for each wideband orpartial-band, and the reporting period is long-term. In Equation 33,ϕ=exp(−j2πn/4) for n=0,1,2,3, ϕ_(n)=exp(−j2πn/8) for n=0,1, . . . ,7corresponding to the phase may be set to QPSK or 8-PSK according to therange of the n value.

Accordingly, the base station may inform the UE of specific informationcorresponding to the a value and/or ϕ_(n) co-phasing size by RRC orpre-agree with the UE. Alternatively, the base station maysignal/configure bit fields for the amplitude and co-phase of thecodebook for the UE individually or integrally and set them for the UE.For example, if the bit field size of the amplitude is set to 1 bit,α={1,0.5} or α={1,0}, and the base station may set the co-phase bitfield size to 2 bits and inform the UE of information on co-phasingbased on QPSK.

The above-explained codebook may assume X-pol and be more suitable whenthe same analog beam is configured/applied for each port. On the otherhand, if different analog beams are configured/applied for each port, itmay be ambiguous to know which port is given a better beam gain due tothe differences in beam gain. Thus, a codebook having such a structureas in Equation 34, which is a more generalized form of the proposedcodebook, may be suggested. According to this codebook, the poweramplitude codebook of each port may be configured independently, therebyimproving performance gain.

$\begin{matrix}{{{\frac{1}{\sqrt{\alpha^{2} + \beta^{2}}}\begin{bmatrix}\alpha \\{\beta \; \varphi_{n}}\end{bmatrix}}\mspace{14mu} {for}\mspace{14mu} {Rank}\mspace{14mu} 1}{{\frac{1}{\sqrt{2( {\alpha^{2} + \beta^{2}} )}}\begin{bmatrix}\alpha & \beta \\{\beta \; \varphi_{n}} & {- {\alpha\varphi}_{n}}\end{bmatrix}}\mspace{14mu} {for}\mspace{14mu} {Rank}\mspace{14mu} 2}} & \lbrack {{Equation}\mspace{14mu} 34} \rbrack\end{matrix}$

In the codebook according to Equation 34, the values of parameters(α,β,ϕ_(n)) (and/or each parameter set and/or set size) may be set byRRC or pre-agreed between the base station and the UE. Alternatively,when the UE reports a port index with a relatively high gain in 1 bit tothe base station to reduce the feedback bits of α,β, the base stationmay set the amplitude coefficient of the corresponding reported port to‘1’. In this case, the UE reports only the amplitude coefficientinformation of the other one port to the base station, and as a result,the feedback bits are reduced. For example, in a case where the UE givesfeedback/report of a port index with a high gain as the second port, β=1is determined/set, and a may be determined/set to a value the UE reportsto the base station, within an amplitude set (e.g., α={1,0.5,0.25,0})pre-agreed between the base station and the UE.

To apply the aforementioned 2-port codebooks to a unified framework ofthe dual-stage structure, W1 (matrix) may be assumed as a square matrix(I), and the codebooks of Table 4 or Table 5 may be applied as W2(matrix) (i.e., W=W1*W2=1*W2). In another method, the aforementionedanalog beam selection codebooks may be used for W1, and W2 may beconfigured as in Table 4 and Table 5 so that codebooks aredefined/applied in the form of W=W1*W2=Wa*W2. For Wa, the aforementionedTx analog codebook configuration may be used. In another method, Wa maybe N_(a,Tx) analog beam selection codebooks. For example, forN_(a,Tx)=4, selection codebooks of Wa may be configured/defined as(e_(i),e_(j))∈{(i,j)|(1,1),(2,2),(3,3),(4,4),(1,2),(1,3),(1,4),(2,3),(2,4),(3,4)},or a set of some of them to adjust to the payload size—for example,(e_(i),e_(j))∈{(i,j)|(1,1),(2,2),(3,3),(4,4),(1,2),(1,4),(2,3),(2,4)}, abeam selection combination of LTE-A rank 2 codebooks. Alternatively, forN_(a,Tx)=4, selection codebooks of Wa may be specialized for Table 5 andconfigured/defined/transmitted by using different beams for differentports (in the above example,(e_(i),e_(j))∈{(i,j)|(1,2),(1,3),(1,4),(2,3),(2,4),(3,4)}).

In another method for configuring a 2-port codebook, W2 in W=Wa*W2 maybe configured by a linear combining codebook. For example, W2 may beconfigured as in

${\frac{1}{\sqrt{{c_{1}}^{2} + {c_{2}}^{2}}}( {\begin{bmatrix}c_{1} \\0\end{bmatrix} + \begin{bmatrix}0 \\c_{2}\end{bmatrix}} )},$

and c1 and c2 have a complex value.

The base station may configure which of the aforementioned codebooks theUE will use/apply by RRC.

Proposal 3) Panel-Based Codebook

One of the new characteristics of the New RAT is to support amulti-panel antenna array consisting of multiple antennas as shown inFIG. 20. In this case, as shown in FIG. 20, unless the spacing betweenpanels is set in such a manner that the spacing between all antennaelements is constant, the characteristics (i.e., uniform increments) ofDFT codebooks which the existing LTE is based on, are not met, therebyleading to performance degradation.

To solve this, the present invention proposes a method (proposal 3-1)that performs compensation between each panel and/or a method (proposal3-2) that selects a specific panel(s) and configures a digital codebook.

3-1) Compensation Between Panels

For convenience of explanation, this embodiment will be described withreference to FIG. 20.

In FIG. 20, ports may be configured for each panel by 4-element verticalantenna virtualization, with each panel (panels 1 through 4) including 8ports, and therefore a total of 32 digital ports are configured. 32ports are supported in eFD-MIMO, and class A codebooks may be used. Inthis case, the final codebook may be as in Equation 35:

$\begin{matrix}{W = {{W_{c}W_{1}W_{2}} = {\underset{\underset{Wc}{}}{\begin{bmatrix}{\overset{\sim}{W}}_{c} & 0 \\0 & {\overset{\sim}{W}}_{c}\end{bmatrix}}\underset{\underset{W_{1}}{}}{\begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix}}\underset{\underset{W_{2}}{}}{\begin{bmatrix}e_{i\; 2} \\{\varphi_{n}e_{i\; 2}}\end{bmatrix}}}}} & \lbrack {{Equation}\mspace{14mu} 35} \rbrack\end{matrix}$

where {tilde over (w)}_(c)∈C^(N) ¹ ^(N) ² ^(×N) ¹ ^(N) ² is a diagonalmatrix and serves to perform codebook compensation control (i.e.,compensation matrix/codebook), W₁∈C^(2N) ¹ ^(N) ² ^(×2N) ^(W1) is W1 ofa dual-stage codebook in a LTE system, N_W1 corresponds to the number ofbeam groups of W1, and W₂∈C^(2N) ^(W1) ^(×rank) is W2 of the dual-stagecodebook in the LTE system and serves to perform beam selection andco-phasing.

Referring to FIG. 20, assuming that (N1′=4, N2′=1) N2 direction is avertical direction, We may be configured as in Equation 36:

$\begin{matrix}{{{\overset{\sim}{W}}_{c} = \begin{bmatrix}{\overset{\sim}{W}}_{1c} & 0 \\0 & {\overset{\sim}{W}}_{2c}\end{bmatrix}},{{\overset{\sim}{W}}_{1c} = \begin{bmatrix}1 & \; & \; & \; & \; & \; & \; & \; \\\; & \alpha & \; & \; & \; & \; & \; & \; \\\; & \; & 1 & \; & \; & \; & \; & \; \\\; & \; & \; & \alpha & \; & \; & \; & \; \\\; & \; & \; & \; & 1 & \; & \; & \; \\\; & \; & \; & \; & \; & \alpha & \; & \; \\\; & \; & \; & \; & \; & \; & 1 & \; \\\; & \; & \; & \; & \; & \; & \; & \alpha\end{bmatrix}},{{\overset{\sim}{W}}_{2c} = \begin{bmatrix}\beta & \; & \; & \; & \; & \; & \; & \; \\\; & \gamma & \; & \; & \; & \; & \; & \; \\\; & \; & \beta & \; & \; & \; & \; & \; \\\; & \; & \; & \gamma & \; & \; & \; & \; \\\; & \; & \; & \; & \beta & \; & \; & \; \\\; & \; & \; & \; & \; & \gamma & \; & \; \\\; & \; & \; & \; & \; & \; & \beta & \; \\\; & \; & \; & \; & \; & \; & \; & \gamma\end{bmatrix}},} & \lbrack {{Equation}\mspace{14mu} 36} \rbrack\end{matrix}$

where α, β, γ refer to compensation terms/compensators/correctors(hereinafter, ‘correctors’) of panels 2, 3, and 4 (with respect to panel1)—for example, they may have a particular complex value such asQPSK{1,−1,j,−j} and/or BPSK(binary phase-shift keying)). Thesecorrectors may be used to compensate for the phase and/or amplitudebetween panels, and the UE may signal the correctors (e.g., α, β, γ) andgive report/feedback to the base station by CSI (e.g., PMI in CSI). Inthis case, the UE may give report/feedback indicating that a correctoris WB (Wideband) and/or SB (Subband) according to the RRC mode setting(e.g., modes 1 and 2) by the base station (that is, the UE reports tothe base station about a corrector (hereinafter, described as “WB and/orSB panel corrector’) selected/derived/acquired for Wideband and/orSubband according to the mode setting).

If γ can be expressed by a function of α and β due to thecharacteristics of a linear planar array (for example, γ=α*β), the UEmay not give feedback on γ and therefore the feedback overhead isreduced.

The above concept may be expanded to designate one representative panelcorrector value for each domain. In the above example, a may bedesignated as a vertical panel reference corrector, and β may bedesignated as a horizontal panel reference corrector, and the correctorsfor the other panels may be expressed by a function of α and/or β. Forexample, if panel 5 exists at the right side of panel 3 of FIG. 20, thephase corrector (compensation value) of panel 5 may be expressed by afunction of α, as in f(a)=α², for example.

Although the corrector may have maximum performance when feedback isgiven in SB and/or short-term periods, the feedback overhead may besaved by giving report/feedback in the same period as W1 PMI or ininteger multiples thereof. The configuration of a matrix (compensationmatrix) for the corrector may affect the method of indexing between allthe panels and ports. Therefore, the port indexing direction may bepre-agreed between the base station and the UE or indicated to the UE byhigher-layer signalling.

In another compensation method, compensation may be performed on a portor panel sub group in a panel that maintains the linear incrementsbetween antenna ports. This can be mathematically expressed by Equation37:

$\begin{matrix}{W = {{W_{c}W_{1}W_{2}} = {{{\quad\quad}\begin{bmatrix}I & 0 & \; & \; & \cdots & \; & \; & 0 \\0 & {\alpha \; I} & \; & \; & \; & \; & \; & \; \\\; & \; & {\beta \; I} & \; & \; & \ddots & \; & \; \\\; & \; & \; & {\gamma \; I} & \; & \; & \; & \vdots \\\vdots & \; & \ddots & \; & I & \; & \; & \; \\\; & \; & \; & \; & \; & {\alpha \; I} & \; & \; \\\; & \; & \; & \; & \; & \; & {\beta \; I} & 0 \\0 & \; & \; & \cdots & \; & \; & 0 & {\gamma \; I}\end{bmatrix}}{{{\quad\quad}\begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 & \; & \; & \cdots & \; & \; & 0 \\0 & {\overset{\sim}{W}}_{2} & \; & \; & \; & \; & \; & \; \\\; & \; & {\overset{\sim}{W}}_{3} & \; & \; & \ddots & \; & \; \\\; & \; & \; & {\overset{\sim}{W}}_{4} & \; & \; & \; & \vdots \\\vdots & \; & \ddots & \; & {\overset{\sim}{W}}_{1} & \; & \; & \; \\\; & \; & \; & \; & \; & {\overset{\sim}{W}}_{2} & \; & \; \\\; & \; & \; & \; & \; & \; & {\overset{\sim}{W}}_{3} & 0 \\0 & \; & \; & \cdots & \; & \; & 0 & {\overset{\sim}{W}}_{4}\end{bmatrix}}\begin{bmatrix}e_{1} \\e_{2} \\e_{3} \\e_{4} \\{\varphi_{n}e_{1}} \\{\varphi_{n}e_{2}} \\{\varphi_{n}e_{3}} \\{\varphi_{n}e_{4}}\end{bmatrix}}}}} & \lbrack {{Equation}\mspace{14mu} 37} \rbrack\end{matrix}$

where W_(c)∈C^(N) ¹ ^(N) ² ^(×N) ¹ ^(N) ² , {tilde over (W)}₁∈C^(N′) ¹^(N′) ² ^(×N′) ^(W1) is defined as a W1 fat matrix configured by thenumber of ports set within one panel, and I∈C^(N′) ¹ ^(N′) ² ^(×N′) ¹^(N′) ² . Also, W2 is a matrix that performs beam selection andco-phasing for each panel, which has been described assuming rank 1 inthe above example but not limited thereto and may be expanded to ageneral W2 expression.

In the example described above and example to be described later, theco-phase is described as configured/reported alike for each panel forconvenience of explanation, but it is needless to say that the co-phasemay be configured/reported independently for each panel for performanceimprovement.

According to the method according to Equation 37, the following twocases may be taken into consideration: i) {tilde over (w)}₁≠{tilde over(w)}₂≠{tilde over (w)}₃≠{tilde over (w)}₄ and ii) {tilde over(w)}₁={tilde over (w)}₂={tilde over (w)}₃={tilde over (w)}₄.

i) As exemplified in FIG. 20, for example, an 8-port codebook is usedfor each panel, and different W1 beam groups are assumed for each panel.Thus, codebook granularity increases significantly, thereby increasingperformance gain. However, the calculation complexity and the number offeedback bits may increase in proportion to the number of panels, ascompared to ii). There is an advantage that complexity and the number offeedback bits can be reduced because of the use of a representative W1beam group for each panel. In this case, as is the case with thecodebooks of Equation 35 and/or 36, α, β, γ for panel compensation mayhave a particular complex value such as QPSK {1,−1,j,−j}, and theirfeedback periods may be equal to a W1 PMI period or integer multiples ofthe W1 PMI period.

According to the method according to Equation 37, an 8-port codebook isassumed for each panel, and Equation 37 may also apply to two 16-portpanel sub-groups consisting of panels 1 and 2 and panels 3 and 4,respectively, in FIG. 20. To this end, the UE may additionally reportinformation on the panel sub-groups to the base station. For example, ifthe base station informs the UE of the number of panels of each panelsub-group and the number of panels along the horizontal or verticaldirection in each panel sub-group, then the UE may select a specificpanel sub-group and report it to the base station. This sub panel group(i.e., the sub panel group reported by the UE) may be used for eachdigital codebook application, or may be used for the purpose ofindicating a group to which the same analog beam is applied.

In a case where digital precoding is configured for each panel or foreach sub panel group as in Equation 37, it may be desirable that portindexing is performed preferentially on “ports having the samepolarization within one panel” in order to facilitate codebookconfiguration.

3-2) Panel/Sub Panel Group Selection Codebook

When different analog beamforming is performed/applied for each panel orfor each sub panel group, it may be desirable to select a panel or subpanel group corresponding to the best analog beam and give CSI feedback.To this end, the We matrix in Equation 37 may be modified into aselection matrix as shown in Equation 38 and used.

$\begin{matrix}{{W_{s} = {\begin{bmatrix}{\rho \; I} & 0 & \; & \; & L & \; & \; & 0 \\0 & {\alpha \; I} & \; & \; & \; & \; & \; & \; \\\; & \; & {\beta \; I} & \; & \; & O & \; & \; \\\; & \; & \; & {\gamma \; I} & \; & \; & \; & M \\M & \; & O & \; & {\rho \; I} & \; & \; & \; \\\; & \; & \; & \; & \; & {\alpha \; I} & \; & \; \\\; & \; & \; & \; & \; & \; & {\beta \; I} & 0 \\0 & \; & \; & L & \; & \; & 0 & {\gamma \; I}\end{bmatrix} \in C^{N_{1}N_{2} \times N_{1}N_{2}}}},\rho,\alpha,\beta,{\gamma \in \{ {0,1} \}}} & \lbrack {{Equation}\mspace{14mu} 38} \rbrack\end{matrix}$

where I∈C^(N′) ¹ ^(N′) ² ^(×N′) ¹ ^(N′) ² If only one among ρ, α, β, andγ has a value of 1, single panel selection is performed (2-bit feedbackis required in the above example), and if two or more among ρ, α, β, andγ have a value of 1, multi-panel selection is performed (4-bit feedbackis required in the above example). In the latter case, the UE may expectthat the same analog beam will be transmitted through the selectedmulti-panels.

Hence, when a PMI for panel selection is reported to the base station,the base station will find out that the UE is using only the ports inthe panels corresponding to the reported PMI, and will activate thecorresponding ports and deactivate the other ports for the correspondingUE and use them for other UEs' transmissions.

In the above example, assuming that two panels are selected, a total of2*2*N1′*N2′ ports are activated. In this case, the UE may apply adigital codebook corresponding to the 2*2*N1′*N2′ ports and give aPMI/CQI/RI report. If a non-uniform port layout is configured by theUE's panel selection, a codebook, combined with the above-explainedmethod of compensation between ports, may be applied/used forperformance improvement.

When describing this embodiment in association with the base station'scapability, if the base station has good calibration between panels, itmay be desirable for it to perform digital beamforming using all of the2*2*N1′*N2′ ports. On the contrary, if the base station has no goodcalibration between panels, it may be desirable for it to performdigital beamforming on 2*N1′*N2′ ports or NP*2*N1′*N2′ portscorresponding to one panel or a specific NP number of panels. That is, anon-calibrated base station may indicate to the UE to configure/applythe panel selection codebook so as to prevent digital beamformingthrough port aggregation between panels. Alternatively, the UE, if ithas a sufficiently high gain by analog beamforming thanks to a goodgeometry, may not highly require digital beamforming, and the UE mayselect a preferred panel(s) by using a panel selection codebook in orderto reduce the complexity of codebook calculation.

To make the aforementioned panel selection codebook work properly, thebase station may inform the UE of information about at least one amongN1, N2, N1′, and N2′ by RRC or pre-agree with the UE. Moreover, theaforementioned codebooks may be used individually or in combination. Inthe latter case, for example, an analog beam selection codebook and apanel selection codebook may be used in combination. This example mayapply when different analog beams are applied to different panels.

3-3) Panel/Sub Panel Group Combination Codebook

When a panel linear combination codebook is configured by modifying theaforementioned selection codebook, We may be configured by Equation 39.

$\begin{matrix}{{{{W_{C} = {\begin{bmatrix}{\rho \; I} & {\alpha \; I} & {\beta \; I} & {\gamma I} & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & {\rho \; I} & {\alpha \; I} & {\beta \; I} & {\gamma I}\end{bmatrix} \in C^{2N_{1}^{\prime}N_{2}^{\prime} \times N_{1}N_{2}}}}{W = {{W_{c}W_{1}W_{2}} = \begin{bmatrix}{\rho \; I} & {\alpha \; I} & {\beta \; I} & {\gamma I} & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & {\rho \; I} & {\alpha \; I} & {\beta \; I} & {\gamma I}\end{bmatrix}}}}\quad}{\quad{{\lbrack \begin{matrix}{\overset{\sim}{W}}_{1} & 0 & \; & \; & \cdots & \; & \; & 0 \\0 & {\overset{\sim}{W}}_{2} & \; & \; & \; & \; & \; & \; \\\; & \; & {\overset{\sim}{W}}_{3} & \; & \; & \ddots & \; & \; \\\; & \; & \; & {\overset{\sim}{W}}_{4} & \; & \; & \; & \vdots \\\vdots & \; & \ddots & \; & {\overset{\sim}{W}}_{1} & \; & \; & \; \\\; & \; & \; & \; & \; & {\overset{\sim}{W}}_{2} & \; & \; \\\; & \; & \; & \; & \; & \; & {\overset{\sim}{W}}_{3} & 0 \\0 & \; & \; & \cdots & \; & \; & 0 & {\overset{\sim}{W}}_{4}\end{matrix} \rbrack\lbrack \begin{matrix}e_{1} \\e_{2} \\e_{3} \\e_{4} \\{\varphi_{n}e_{1}} \\{\varphi_{n}e_{2}} \\{\varphi_{n}e_{3}} \\{\varphi_{n}e_{4}}\end{matrix} \rbrack} = {\quad\begin{bmatrix}{{\rho {\overset{\sim}{W}}_{1}e_{1}} + {\alpha {\overset{\sim}{W}}_{2}e_{2}} + {\beta {\overset{\sim}{W}}_{3}e_{3}} + {\gamma {\overset{\sim}{W}}_{4}e_{4}}} \\{\varphi_{n}( {{\rho {\overset{\sim}{W}}_{1}e_{1}} + {\alpha {\overset{\sim}{W}}_{2}e_{2}} + {\beta {\overset{\sim}{W}}_{3}e_{3}} + {\gamma {\overset{\sim}{W}}_{4}e_{4}}} )}\end{bmatrix}}}}} & \lbrack {{Equation}\mspace{14mu} 39} \rbrack\end{matrix}$

Referring to Equation 39, the length of a column in the dimension of thefinal codebook is set to 2*N1′*N2′, and this may beunderstood/interpreted that analog and digital beamformed vectors withthe length of 2*N1′*N2′ for each port are combined.

In the above method, the values of ρ, α, β, and γ may be expressed byρ=a_(a)exp(jψ_(a)),α=a_(b)exp(jψ_(b)),β=α_(c)exp(jψ_(c)),γ=a_(d)exp(jψ_(d)),for example. In this case, the amplitude component(a_(a),a_(b),a_(c),a_(d)) and the phase component(ψ_(a),ψ_(b),ψ_(c),ψ_(d)) may be reported independently or integrally.In an independent report, for example, the UE may report the amplitudecomponent as wideband (or partial-band)/long-term and the phasecomponent as wideband/subband, individually. Because a combination isdone, the amplitude (a) may be set to one of the values {1,0.5,0.25,0},and the phase(ψ) may be set to one of the values QPSK {1,−1,j,−j}.

To save the payload size, the number of combined panels may be limitedto a specific number, and this number of panels may be signalled byRRC(or MAC(Medium Access Control) CE(Control Element)) or may bepre-agreed between the UE and the base station. That is, in the aboveexample, if the number of combined panels is assumed to be 2, the UE mayreport the power index 0 for the least preferred two panel indices ormay select two panels first at the front end of the panel combinationcodebook. That is, in a case where two beams out of four panel beams arecombined, if indices are allocated for each combination of panels, as in{(1,2), (1,3), (1,4), (2,3), (2,4), (3,4)}, the UE may first report aparticular index selected by them to the base station and then performthe panel combination codebook for the selected panels. Moreover, it maybe inefficient to report each value corresponding all power combiningcoefficients. Thus, the power combining coefficient for a particularpanel (i.e., a panel with the highest beam gain or the first panel asdefault) may be assumed/set to be a specific value, and the UE mayreport only the power combining coefficient for the other combined beam.For example, if the power of the first panel is assumed to be ‘1’, theUE may report the amplitude values of α, β, and γ corresponding to theother panel.

In the panel combination codebook proposed above, the base station mayconfigure whether the UE will use the same codebook or phasecompensation (WB and/or SB) for each panel or different codebooks orphase combinations for each panel.

In the case of a codebook with different beam groups for eachpolarization, if the above-explained panel compensation codebook isapplied, the values of ρ, α, β, and γ may be set/applied independentlyfor each polarization. That is, ρ_1, α_1, β_1, and γ_1 for the firstpolarization and ρ_2, α_2, β_2, and γ_2 for the secondpolarization—i.e., a total of 8 independent variables—may be used toperform panel compensation.

Similarly to the method proposed above, a codebook forindicating/reporting a differential in compensation value between apanel and a reference panel may be considered/proposed.

The proposed compensation codebook may be extensively applied as an SBpanel correction codebook, as well as a WB panel correction codebook.This may increase the payload for SB CSI feedback, but a panelcalibration codebook may be applied for each SB, which reflectsfrequency selectivity better and therefore leads to a very largeimprovement in performance. However, to solve the problem of the payloadincrease, the feedback granularity/unit/size/bit-width of the SB panelcorrector may be set/defined differently from the feedbackgranularity/unit/size/bit-width of the WB panel corrector. Particularly,to reduce feedback overhead, the feedbackgranularity/unit/size/bit-width of the SB panel corrector may beset/defined to be smaller than the feedbackgranularity/unit/size/bit-width of the WB panel corrector (that is, thefeedback granularity of the SB panel corrector is lower than thefeedback granularity of the WB panel corrector). For example, thefeedback granularity/unit/size/bit-width of the WB panel corrector maybe set to 2 bits (in QPSK), and the feedbackgranularity/unit/size/bit-width of the SB panel corrector may be set to1 bit (in BPSK).

In this case, the UE may give the base station a recommendation/feedbackabout whether to use the WB and/or SB panel correction codebook. And/or,the base station may configure whether or not the UE uses the WB and/orSB panel correction codebook by RRC configuration. For example, theapplication of the WB panel correction codebook may be defined as afirst mode, and the application of both the WB and SB panel correctioncodebooks may be defined as a second mode, and the base station mayindicate to the UE which mode to apply through specific RRC signalling(e.g., ‘CodebookMode’). When the first mode is set, the UE may report tothe base station the WB panel corrector selected/derived based on QPSKin a 2-bit size by CSI (particularly, PMI). When the second mode is set,the UE may report to the base station the WB panel correctorselected/derived based on QPSK in a 2-bit size and the SB panelcorrector selected/derived based on BPSK in a 1-bit size by CSI(particularly, PMI). In the second mode, the WB panel corrector may beused to compensate for the overall co-phase, and the SB panel correctormay be used to compensate for the overall co-phase, and the SB panelcorrector may be used to finely compensate for the co-phase.

Alternatively, whether to use the WB panel correction codebook or the SBpanel correction codebook may be tied to the number (=Mg*Ng) of panelsof the base station. For example, for Mg*Ng=4, the number N_W1 of beamsof W1 in a digital codebook may be set/applied to 1, and, for Mg*Ng=2,the number N_W2 of beams of W1 in a digital codebook may be set/appliedto 2 (N_W1=2).

While the proposed codebook has been described with respect to DL, it isnot limited thereto but may be readily and extensively applicable to ULcodebook configuration.

Hereinafter, Type 1 codebook configuration assuming a single panel willbe described.

First of all, the use of the same beam group will be described, whichmay be expressed as in Equation 40:

$\begin{matrix}{W_{1} = \begin{bmatrix}B & 0 \\0 & B\end{bmatrix}} & \lbrack {{Equation}\mspace{14mu} 40} \rbrack\end{matrix}$

where W1 performs beam grouping with WB/long-term characteristics in thedual-stage codebook. In this case, B∈C^(N) ¹ ^(N) ² ^(×L), and B mayhave L values (e.g., L=1,2,4,7, . . . ). Although N_W1 has been usedbefore indicating the number of beam groups of W1, it will behereinafter replaced with L. Now, a description will be given of a casewhere the UE selects L beams.

The UE may freely and explicitly indicate L beams being used to the basestation in an explicit fashion (e.g., in bitmap form or by indicatingthe beam index). In this case, the number of required bits isL*N1*N2*O1*O2 or ┌log₂(LN₁N₂O₁O₂)┐, and there is a problem that thefeedback bits increase as L and the number of Tx antenna portsincreases. Accordingly, the UE may freely select beams within a specificGoB (Grid of Beams) as a way to cut down the number of feedback bits. Anexample of this will be described below with reference to FIG. 21.

FIG. 21 is a view illustrating GoB for N1=4, O1=4, N2=2, and O2=4according to an exemplary embodiment of the present invention.

Referring to FIG. 21, when a beam selection window of 4 by 6 isconfigured, the UE may freely select L−1 beams within this window. Inthis case, the UE may give feedback about the position of aprimary/leading beam 2101 and the window size of 4 by 6.

In another method, an exemplary embodiment of FIG. 22 may be applied.

FIG. 22 is a view illustrating a window configuration method for N1=4,O1=4, N2=2, and O2=4 according to an exemplary embodiment of the presentinvention.

Referring to FIG. 22, the entire GoB is divided into windows of a sizerecommended/fed back by the base station or UE, and the UE may givefeedback on the index (position) of a window and/or information on theselection of L beams freely selected within that window. FIG. 22illustrates the existence of 8 windows of 4 by 6. According to theconfiguration, adjacent windows may overlap. In this case, the basestation may configure information on the positions and/or size of thewindows for the UE.

If the UE selects L beams used for W1, as proposed above, high feedbackbitrate is required. Thus, feedback information (e.g., information onthe selection of L beams) may be limited to using PUCCH reporting,rather than using PUSCH reporting.

Hereinafter, different diagonal matrices forming W1 (i.e., differentbeam groups used for each polarization) will be described, which can beexpressed as in Equation 41.

$\begin{matrix}{W_{1} = \begin{bmatrix}B_{1} & 0 \\0 & B_{2}\end{bmatrix}} & \lbrack {{Equation}\mspace{14mu} 41} \rbrack\end{matrix}$

B_(i)∈C^(N) ¹ ^(N) ² ^(×L) ^(i) (i=1, 2) is defined, L_(i) representsthe number of beams in a beam group of i-slant (e.g., i=1 H slant, andi=2 V slant), and L1 and L2 may have different values (e.g., L1=1, andL2=2). The base station may pre-agree with the UE about the L1 and L2values, or may configure these values for the UE by a higher layer(e.g., RRC or MAC CE). Alternatively, the UE may give the base station arecommendation/feedback about information on the L1 and L2 values.

Configuring W1 as above has the advantage of applying the best codewordfor each polarization but has the disadvantage of significantlyincreasing the feedback overhead of W1. Accordingly, an exemplaryembodiment for solving these disadvantages will be proposed.

Firstly, L₁=L₂ (i.e., if the number of vertical beams and the number ofhorizontal beams are equal) will be described.

In this case, W2 for rank 1 codebook configuration will be proposed asin Equation 42.

$\begin{matrix}{W_{2} = \begin{bmatrix}e_{i} \\{\varphi_{n}e_{j}}\end{bmatrix}} & \lbrack {{Equation}\mspace{14mu} 42} \rbrack\end{matrix}$

where i≠j, j∈{1, . . . ,L} and ϕ_(n)={1,j,−1,−j} are defined, and e_(i)represents a selection vector whose length is L and whose ith elementhas a value of 1 and the other elements has a value of 0. In this case,i and j must be reported individually, and twice as much feedbackoverhead is consumed for beam selection as compared to when the samebeam group is used. For this design, i, j, and co-phase values may bereported as SB. To reduce the SB feedback overhead for beam selection,L1=L2=1 should be satisfied. In this case, W2 may be set to

$W_{2} = {\begin{bmatrix}1 \\\varphi_{n}\end{bmatrix}.}$

In another method, the UE may give report/feedback about i11 and i12 forB1 and give additional report/feedback about the differential between B1and B2. Here, i11 and i12 represent the first and second domain indicesof W1 PMI as in LTE codebooks. That is, the UE may give feedback/reportto the base station about how far B2 is spaced apart from the leadingbeam indices i11 and i12 of B1 in the first and second domains. Forexample, when the leading beam index (i11, i12) of B1 is (10,2) and avalue corresponding to (2.4) as the differential of B1 is additionallyreported/fed back to the base station, the base station may recognizethe leading beam (i11, i12) of B2 as (12,6) and configure B2.

In this method of indicating the differential between B1 (index) and B2(index), the differential may be agreed between the UE and the basestation as a specific value for each domain, or the base station mayconfigure the differential for the UE, or the UE may givereport/feedback to the base station. To reduce the report/feedbackoverhead, the UE may give feedback only about information on thespecific domain (e.g., first or second domain). In this case, the basestation may configure the specific domain for the UE, or the UE mayinform the base station of the specific domain.

The rank 2 codebook configuration may be expressed as in Equation 43:

$\begin{matrix}{W_{2} = \begin{bmatrix}e_{i} & e_{k} \\{\varphi_{n}e_{j}} & {{- \varphi_{n}}e_{l}}\end{bmatrix}} & \lbrack {{Equation}\mspace{14mu} 43} \rbrack\end{matrix}$

As can be seen from Equation 43, variables of i, j, k, and l should meetthe following conditions to maintain the orthogonality for each layer inthe rank 2 codebook.

1. e_(i)=e_(k), e_(j)=e_(l): In this case, the codebook indicates thatthe same beam is selected for each polarization when configuring alayer. When configuring the codebook, ϕ_(n) may be limited toϕ_(n)={1,j}, for example. In this case, beams forming the codebook maybe normalized to 1.

2. {e_(i)≠e_(k)}, {e_(j)≠e_(l)}: In this case, B1 of W1 should beconfigured for each polarization so that beams selected by i and k areorthogonal to each other, and B2 of W1 should be configured for eachpolarization so that beams selected by j and l are orthogonal to eachother. That is, beam groups of B1 and B2 of W1 should consist of beamsorthogonal to each other. Alternatively, if there are somenon-orthogonal beams, the codebook may be configured by pairingorthogonal beams in the above method. For example, for B₁=[b₀ b₁ b_(O) ₁b_(l+O) ₁ ], assuming that b₀,b_(O) ₁ are orthogonal to each other andb₁,b_(l+O) ₁ are orthogonal to each other, b₀,b_(O) ₁ and b₁,b_(l+O) ₁may be paired according to the above second method—that is, pairing maybe done two times in total. In this method, co-phase ofϕ_(n)={1,j,−1,−j} may be used.

Hereinafter, L₁≠L₂ will be discussed. In this case, a codebook may beconfigured by extensively applying the above method proposed for L₁=L₂.

As a special example of L₁≠L₂, L1=1 will be described first. In thiscase, the rank 1 configuration of W2 is as shown in Equation 44:

$\begin{matrix}{W_{2} = \begin{bmatrix}e_{1} \\{\varphi_{n}e_{i}}\end{bmatrix}} & \lbrack {{Equation}\mspace{14mu} 44} \rbrack\end{matrix}$

In this case, beam selection and co-phasing are possible for beamscorresponding to one slant. Thus, a PMI may be determined/indicatedindependently for each polarization, thereby increasing codebookgranularity and improving performance. In this case, ϕ_(n)={1,j,−1,−j}may be used.

When designing the codebook as above, the codebook may be configured insuch a way that B₁⊂B₂ is established (that is, L beams of B2 alwaysinclude B1) to form a super-set of LTE Class A codebook Config 1.Alternatively, the UE may recommend information on B2 to the basestation.

Similarly, rank 2 codebook may be configured as in Equation 45:

$\begin{matrix}{W_{2} = \begin{bmatrix}1 & 1 \\{\varphi_{n}e_{i}} & {{- \varphi_{n}}e_{j}}\end{bmatrix}} & \lbrack {{Equation}\mspace{14mu} 45} \rbrack\end{matrix}$

For e_(i)=e_(j), ϕ_(n)={1,j} may be used, and for e_(i)≠e_(j), if beamsselected as i and j are orthogonal to each other, ϕ_(n)={1,j,−1,−j} maybe used. Alternatively, co-phase with the same granularity may beapplied to both of the two cases.

In the above-explained method, WB co-phase for beams of B₂ may bereported along with the B2 index. That is, {tilde over (B)}₂=ψ_(n)B₂ maybe set, and W1 may be configured as in Equation 46.

$\begin{matrix}{W_{1} = \begin{bmatrix}B_{1} & 0 \\0 & {\overset{\sim}{B}}_{2}\end{bmatrix}} & \lbrack {{Equation}\mspace{14mu} 46} \rbrack\end{matrix}$

where ψ_(n) is a WB co-phase value, for example, ψ_(n)={1,j,−1,−j}. Inthis case, SB co-phase may be configured as in

${\varphi_{n} = \{ {\frac{1 + j}{\sqrt{2}},\frac{1 - j}{\sqrt{2}},\frac{{- 1} + j}{\sqrt{2}},\frac{{- 1} - j}{\sqrt{2}}} \}},$

for example, to have a different co-phase from WB, thereby increasingcodebook granularity. To save SB feedback bits, the UE may report2-level co-phase by using 1-bit co-phase

$( {{e.g.},{\varphi_{n} = \{ {1,\frac{l + j}{\sqrt{2}}} \}}} ).$

The proposed method is readily applicable to B₁=B₂, and B1 and B2 of W1may be configured/applied independently for each band (or band group).

As described above, similarly to the method of using different beamgroups for each polarization, the SB size may be reduced to increase theaccuracy of SB PMI. Once the SB size is reduced, PMI per SB can be moreaccurate but feedback overhead increases. Accordingly, the base stationmay configure, for the UE, whether to reduce the SB size and/or use acodebook of B₁≠B₂.

A new codebook may be configured by combining the above-proposedcodebook designs.

FIG. 23 is a flowchart illustrating a method for a UE to report CSIaccording to an exemplary embodiment of the present invention. Regardingthis flowchart, the foregoing embodiments/descriptions may apply equallyor similarly, and redundant explanation will be omitted.

First of all, the UE may measure a CSI-RS transmitted from the basestation through multiple panels (S2310).

Next, the UE may report to the base station CSI generated based on theCSI-RS measurement (S2320).

In this case, if the UE reports a WB panel corrector and SB panelcorrector for the multiple panels as the CSI (according to the CSIsettings by the base station), the WB panel corrector and the SB panelcorrector may be reported with different bit widths. Here, the WB panelcorrector may correspond to a beam/codebook phase corrector for eachpanel derived/determined/selected based on the measurement of CSI-RS(resources) for WB, and the SB panel corrector may correspond to abeam/codebook phase corrector for each panel derived/determined/selectedbased on the measurement of CSI-RS (resources) for SB (or for each SB).That is, the WB panel corrector and the SB panel corrector may be usedfor phase correction between the multiple panels. The number of panelsmay be set by higher-layer signalling.

Particularly, the bit width of the SB panel corrector may be shorterthan the bit width of the WB panel corrector—for example, the bit widthof the SB panel corrector may be set to 1 bit, and the bit width of theWB panel corrector may be set to 2 bits. Thus, the WB panel correctormay be reported based on QPSK, and the SB panel corrector may bereported based on BPSK. If the UE reports only the WB panel corrector asthe CSI, the WB panel corrector may be reported with a bit width of 2bits. Whether to report both the WB panel corrector and the SB panelcorrector or only the WB panel corrector may be determined according tothe mode set by the base station (e.g., the mode set by RRC signalling).For example, if the base station indicates mode ‘1’ to the UE, the UEmay recognize that only the WB panel corrector is reported, and if thebase station indicates mode ‘2’, the UE may recognize that both the WBpanel corrector and the SB panel corrector are reported.

The WB panel corrector and the SB panel corrector may be included in aPMI within the CSI when reported. Also, the WB panel corrector and theSB panel corrector may be reported independently for each of theplurality of panels.

General Devices to which the Present Invention is Applicable

FIG. 24 illustrates a block diagram of a wireless communication systemaccording to an exemplary embodiment of the present invention.

Referring to FIG. 24, the wireless communication system includes a basestation 2410 and a plurality of UEs 2420 located within the region ofthe base station 2410.

The base station 2410 includes a processor 2411, a memory 2412, and anRF (radio frequency) unit 2413. The processor 2411 implements thefunctions, processes and/or methods proposed above. The layers ofwireless interface protocol may be implemented by the processor 2411.The memory 2412 is connected to the processor 2411, and stores varioustypes of information for driving the processor 2411. The RF unit 2413 isconnected to the processor 2411, and transmits and/or receives radiosignals.

The UE 2420 includes a processor 2421, a memory 2422, and an RF unit2423. The processor 2421 implements the functions, processes and/ormethods proposed above. The layers of wireless interface protocol may beimplemented by the processor 2421. The memory 2422 is connected to theprocessor 2421, and stores various types of information for driving theprocessor 2421. The RF unit 2423 is connected to the processor 2421, andtransmits and/or receives radio signals.

The memories 2412 and 2422 may be located interior or exterior to theprocessors 2411 and 2421, and may be connected to the processors 2411and 2421 by well-known various means. In addition, the base station 2410and/or the UE 2420 may have a single antenna or multiple antennas.

The above-described embodiments correspond to combinations of elementsand features of the present invention in prescribed forms. And, therespective elements or features may be considered as selective unlessthey are explicitly mentioned. Each of the elements or features can beimplemented in a form failing to be combined with other elements orfeatures. Moreover, it is able to implement an embodiment of the presentinvention by combining elements and/or features together in part. Asequence of operations explained for each embodiment of the presentinvention can be modified. Some configurations or features of oneembodiment can be included in another embodiment or can be substitutedfor corresponding configurations or features of another embodiment. And,it is apparently understandable that an embodiment is configured bycombining claims failing to have relation of explicit citation in theappended claims together or can be included as new claims by amendmentafter filing an application.

In the present description, “A and/or B” can be interpreted as “at leastone of A and B”.

The embodiments of the present invention may be implemented by variousmeans, for example, hardware, firmware, software and the combinationthereof. In the case of the hardware, an embodiment of the presentinvention may be implemented by one or more application specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), a processor, a controller, amicro controller, a micro processor, and the like.

In the case of the implementation by the firmware or the software, anembodiment of the present invention may be implemented in a form such asa module, a procedure, a function, and so on that performs the functionsor operations described so far. Software codes may be stored in thememory, and driven by the processor. The memory may be located interioror exterior to the processor, and may exchange data with the processorwith various known means.

It will be understood to those skilled in the art that variousmodifications and variations can be made without departing from theessential features of the inventions. Therefore, the detaileddescription is not limited to the embodiments described above, butshould be considered as examples. The scope of the present inventionshould be determined by reasonable interpretation of the attachedclaims, and all modification within the scope of equivalence should beincluded in the scope of the present invention.

MODE FOR INVENTION

A variety of embodiments of the present invention have been described inthe best mode for carrying out the invention.

INDUSTRIAL APPLICABILITY

While the present invention has been described mainly with respect to anexample of application of 3GPP LTE/LTE-A systems, it may be applied tovarious wireless communication systems, in addition to the 3GPPLTE/LTE-A systems.

1. A method for reporting channel state information (CSI) of a terminalin a wireless communication system, the method comprising: measuring aCSI-RS (reference signal) transmitted from a base station throughmultiple panels from a base station; and reporting the CSI generatedbased on the CSI-RS measurement to the base station, wherein, a WB(Wideband) panel corrector and a SB (Subband) panel corrector arereported with different bit widths, when the terminal reports the WBpanel corrector and the SB panel corrector for the multiple panels asthe CSI, and wherein the WB panel corrector and the SB panel correctorare used for phase correction between the multiple panels.
 2. (canceled)3. The method of claim 1, wherein the bit width of the SB panelcorrector is shorter than the bit width of the WB panel corrector. 4.The method of claim 3, wherein the bit width of the SB panel correctoris 1 bit, and the bit width of the WB panel corrector is 2 bits.
 5. Themethod of claim 4, wherein the WB panel corrector is reported based onQPSK (quadrature phase-shift keying), and the SB panel corrector isreported based on BPSK (binary phase-shift keying).
 6. The method ofclaim 4, wherein, when the reporting only the WB panel compensator asthe CSI, the WB panel corrector is reported with the bit-a-bit width of2 bits.
 7. The method of claim 1, wherein a number of the multiplepanels is set by higher-layer signaling.
 8. The method of claim 7,wherein the reporting of the WB panel corrector and/or the SB panelcorrector is set by the higher-layer signalling.
 9. The method of claim7, wherein the WB panel corrector and the SB panel corrector arereported in a PMI (Precoding Matrix Index) in the CSI.
 10. The method ofclaim 7, wherein the WB panel corrector and the SB panel corrector arereported independently for each of the multiple panels and/orpolarizations.
 11. A terminal that receives a channel stateinformation-reference signal (CSI-RS) in a wireless communicationsystem, the terminal comprising: a radio frequency (RF) unit fortransmitting and receiving a radio signal; and a processor forcontrolling the RF unit, wherein the processor measures a CSI-RS(reference signal) transmitted from a base station through multiplepanels, and reports the CSI generated based on the CSI-RS measurement tothe base station, wherein a WB (Wideband) panel corrector and a SB(Subband) panel corrector are reported with different bit widths, whenthe terminal reports the WB panel corrector and the SB panel correctorfor the multiple panels as the CSI, and wherein the WB panel correctorand the SB panel corrector are used for phase correction between themultiple panels.
 12. (canceled)
 13. The terminal of claim 11, whereinthe bit width of the SB panel corrector is shorter than the bit width ofthe WB panel corrector.
 14. The terminal of claim 13, wherein the bitwidth of the SB panel corrector is 1 bit, and the bit width of the WBpanel corrector is 2 bits.
 15. The terminal of claim 14, wherein the WBpanel corrector is reported based on QPSK (quadrature phase-shiftkeying), and the SB panel corrector is reported based on BPSK (binaryphase-shift keying).